DOI 10.1111/poms.13583 © 2021 Production and Operations Management Society Optimal Pricing and Overbooking of Reservations Jaelynn Oh* David Eccles School of Business, The University of Utah, Salt Lake City, Utah 84112, USA, jaelynn.oh@eccles.utah.edu Xuanming Su The Wharton School, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA, xuanming@wharton.upenn.edu e study the optimal design of reservations for a firm with limited capacity. The firm faces a random number of customers, each of whom has a random valuation for service. The reservation policy has two components: pricing and overbooking. For the former, the firm charges a reservation fee (at the time of reservation) and a service price (at the time of service). For the latter, the firm imposes a booking limit that caps the number of reservations it sells. Given the firm’s reservation policy, customers make reservations in advance and later decide whether to show up. Denying service to reservation holders is costly. We obtain the following equilibrium results. First, when demand is small relative to capacity, the firm’s pricing structure relies on reservation fees prepaid in advance, but when demand is large relative to capacity, it relies on payment received upon service. Second, when demand is low and/or predictable, the firm accepts all reservation requests, but when demand is high and/or variable, the firm uses a booking limit. W Key words: pricing; overbooking; reservations; revenue management; advance selling; capacity History: Received: May 2020; Accepted: August 2021 by Dan Zhang, after 2 revisions. *Corresponding author. deposit, and some hotels require a full and nonrefundable payment upon reservation. Second, on overbooking, firms have to decide how many excess reservations to accept beyond the number capacity can accommodate. Denying service to reservation holders can be costly; for example, the Department of Transportation mandates that up to 400% of the oneway fare must be compensated to each involuntarily bumped passenger (DOT 2020). Yet, bumping rates differ across US airlines, ranging from 0.02 to 6.28 per 100,000 passengers in 2018 (McCarthy 2019). By studying the pricing and the overbooking decisions jointly, we hope to answer the following research questions. First, how does the market condition affect the optimal overbooking policy? Second, how can the firm choose the optimal pricing policy among the wide range of reservation pricing policies observed in practice dependent on the market condition? From the answers of the above research questions, we hope to provide recommendations on the optimal overbooking and pricing policies to firms that take reservations while facing the uncertainties on the market size and customer valuations. We analyze the following stylized model. First, the firm determines its reservation policy, which comprises of two prices (a reservation fee and a service price) and a booking limit on the maximum number of reservations to take. Then, the market size is realized; customers decide whether to make reservations 1. Introduction Reservations are ubiquitous for firms such as car rentals, airlines, and hotels. These firms have limited capacity and may take reservations in advance in order to subsequently guarantee service. Because of the time gap between the point reservation is made and the point service is rendered, both the firm and the customers face uncertainty. Firms give out reservations without knowing the precise number of patrons, and customers make reservations before learning their precise need for service. This study intends to study how firms can set the optimal overbooking and pricing policies to deal with the uncertainties the firm and the customers face when reservations are made. As we study the optimal reservation policies, we provide explanations on how certain market conditions, characterized as the average market size and the market size variability, lead to certain equilibrium outcome. In this study, we focus on two specific aspects of reservation policies: pricing and overbooking. First, on pricing, firms generally have to make two decisions: how much to charge for making the reservation and how much to charge for exercising it; these are analogous to the purchase price and strike price of financial options. There is a wide variation observed in practices. For example, some hotels give out reservations for free, others charge a nonrefundable 928 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vol. 31, No. 3, March 2022, pp. 928–940 ISSN 1059-1478|EISSN 1937-5956|22|3103|0928 Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society (paying the reservation fee) and if so, the firm accepts reservations up to its booking limit. Finally, individual customer valuations are realized; customers decide whether to show up (paying the service price) and the firm serves customers up to its capacity limit. This model admits a wide range of reservation policies that are chosen by firms. We summarize our results below. First, the optimal overbooking policy has a simple structure and takes one of two forms. In some cases, it may be optimal to accept all reservation requests and impose no booking limit whatsoever. In other cases, a booking limit is needed: this caps the number of reservations given out so that the number of customers who are expected to show up is aligned with the units of capacity available. Note that the booking limit may exceed capacity, so some overbooking may be practiced. In summary, the optimal overbooking policy may be an “accept all policy” or a “booking limit policy.” Second, the optimal pricing policy often involves a combination of reservation fees and service prices. The former dominates in small markets while the latter dominates in large markets. In extreme cases (i.e., when average market demand is extremely small or extremely large, relative to capacity), it may even be optimal to charge only the reservation fee (i.e., fully prepaid reservations) or only the service price (i.e., free reservations). As the average market size increases, the firm relies less on advance pre-payment at the time of reservation but more on spot payment at the time of consumption. Third, by running numerical simulations, we map the optimal reservation policies with market conditions characterized as a combination of the mean and the standard deviation of the market size. We find that accepting all reservations is an optimal overbooking policy for a market with small mean and/or small variance. On the other hand, setting a booking limit is optimal when the average market size is large and/or the standard deviation of the market size is large. From the numerical results we can also see that the optimal prices alone can effectively regulate the customer traffic when the market size is less variable, but booking limits become essential as the market size variability increases to avoid customer bumping. 2. Literature Review This study is closely related to the advance selling literature. The key feature in common is that customers make purchase decisions while facing uncertainty over their consumption valuations. Despite this uncertainty, DeGraba (1995) finds that limiting supply induces customers to buy in advance, and the threat of unavailability even allows prices to be set 929 above market-clearing levels. Gale and Holmes (1993) show that offering a discount can also induce customers to purchase in advance; this helps shift demand from peak to off-peak periods. Dana (1998) finds that such advance purchase discounts can generate competitive advantages. Xie and Shugan (2001) develop a framework for comparing advance selling to spot selling (i.e., selling to customers after their valuation uncertainty is resolved) and also study whether to advance sell at a discount or at a premium; Shugan and Xie (2005) generalize the earlier framework to competitive settings. Prasad et al. (2011) embed a classic newsvendor model into the advance selling framework to study the firm’s decision of how many units to advance sell; they also compare advance selling and spot selling. Nasiry and Popescu (2012) study how anticipated regret can affect customer decisions and firm profits in an advance selling context. Yu et al. (2015) study the pricing and capacity decision of an advance selling firm when customer valuations are correlated. In this stream of work, the focus is on pure advance selling and pure spot selling, that is, customers make purchase decisions either before or after resolving uncertainty over their valuations. In contrast, we offer a general framework that integrates these two modes of operation: customers pay a reservation fee in advance and/or pay another spot price when they show up for their reservations. Furthermore, we incorporate overbooking into advance selling by allowing the firm to sell more reservations than its capacity can serve. There is a series of related papers that focus on reservations. An early study by Png (1989) finds that optimal reservation policies should provide compensation to reservation holders who show up but are denied service. Bertsimas and Shioda (2003) develop a decision tool for managing restaurant reservations, taking into account the possibility of no-shows. Chen et al. (2017) studies long-term revenue-maximizing admission policy when different types of customers arrive to make reservation requests with services that have heterogeneous duration and start time and the sellers decide which requests to accept or deny. Alexandrov and Lariviere (2012) point out that reservations help attract demand when customers incur a travel cost to request service. Cil and Lariviere (2013) study how to allocate capacity between reservation holders and walk-in demand. Elmaghraby et al. (2009) and Osadchiy and Vulcano (2010) study binding reservations in retail environments: customers may reserve a unit for purchase but are obligated to buy if there is availability at the end of the selling season. In the papers above, the firm sells reservations at a single price. However, we consider a more general mechanism that involves two prices: a reservation fee and a service price. 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Oh and Su: Optimal Pricing and Overbooking of Reservations Oh and Su: Optimal Pricing and Overbooking of Reservations Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society Our two-price modeling setup has alternative interpretations that have been used in some earlier papers. For example, charging a reservation fee in advance and a service price later is equivalent to collecting a partially refundable payment in advance. In the economics literature, Courty and Li (2000) show that a menu of partial refund contracts can be used to screen multiple customer segments: customers who face greater uncertainty are willing to pay more in advance for more generous refunds. Similarly, Akan et al. (2015) apply partial refund contracts to develop a continuous time sequential screening mechanism when selling to customers who realize their valuations at different times. The above papers focus on price discrimination and do not consider the role of capacity constraints, which play a critical role in our study. In this sense, our paper is more closely related to the following revenue management models. Gallego and Sahin (2010) study capacity options: customers pay an option price for the right to purchase a unit of capacity and may later pay the strike price to exercise that right; the option and strike prices here are analogous to our reservation and service fees. The authors focus on profit and welfare implications of capacity options, but we are more interested in understanding the structure of optimal reservations policies (e.g., whether reservations should be fully or partially prepaid). More recently, Georgiadis and Tang (2014) study reservation policies consisting of a nonrefundable deposit and a retail price. They consider four customer segments with low/high service valuations and low/high no-show probabilities, and study the optimal subset of customers to sell reservations to. In contrast, we consider customers who endogenously choose whether to show up for service based on their realized valuations, which follow general distributions. This key difference allows pricing to play a stronger role in regulating customer arrivals in our model. With our model, we distinguish between the following regimes: no reservations (i.e., spot selling), fully refundable reservations, partially refundable reservations, and nonrefundable reservations (i.e., advance selling). While considering advance deposits and spot prices for reservation customers, Oh and Su (2018) study capacity allocation between reservations and walk-ins. This study, on the other hand, studies how to use booking limits to discipline overbooking practices. Finally, our study is related to the literature on appointment scheduling and overbooking. Cayirli and Veral (2003) and Gupta and Denton (2008) provide a comprehensive review of the literature, most of which is in the health care context. Kim and Giachetti (2006) develop an overbooking model that considers both no-shows and walk-ins to obtain the optimal number of appointments. LaGanga and Lawrence (2007), Zeng et al. (2010), and LaGanga and Lawrence (2012) study overbooking models that balance the benefit of expected revenue increase and the cost due to increased customer waits and provider overwork. Robinson and Chen (2010) and Liu et al. (2010) compare appointment overbooking to an open access policy where patients can come right away on the day they want to be seen. Zacharias and Pinedo (2014) find an optimal overbooking policy that minimizes a weighted sum of customer wait time, provider idle time, and provider overtime. Liu and Ziya (2014) look for the optimal panel size (total number of patients the provider commits to provide service for) and study overbooking decisions. The study mentioned above focus on appointment systems with fixed prices. In contrast, we study joint overbooking and pricing decisions. 3. Model The Firm: There is a monopolist firm with a fixed capacity. This capacity may be cars in a car rental company or rooms in a hotel. When capacity is full, no more customers may be served. Let μ denote the firm’s capacity; in other words, the firm can serve no more than μ customers. The firm sells its capacity through reservations. The firm’s reservation policy specifies two prices: a reservation fee ϕ and a service price p. The reservation fee is collected when a reservation is made, and the service price is charged when a reservation holder shows up and receives the service. In addition, the firm sets a booking limit B, which is the maximum number of reservations the firm takes. Note that if the firm takes too many reservations and too many of them show up, the firm will be unable to honor all these reservations. For each reservation holder the firm turns away, the firm arranges a substitute service while incurring a bumping cost C > 0. The firm’s bumping cost C may include a goodwill cost, any cost related to arrangements made to a bumped customer, and a compensation the firm may have to give to a denied customer. There are different practices regarding the compensation in different industries. The hotel industry requires accommodations to be provided at a neighboring hotel at an equal or complementary rate, and they maintain partnerships with neighboring hotels to utilize as alternative arrangements for overbooked customers (Wikipedia 2021). Airlines, however, are mandated to pay an involuntarily bumped customer an amount equal to 200% of the one-way fare upon arranging substitute transportation that is scheduled to arrive within 2 hours after the original arrival time (DOT 2020). The firm does not divulge overbooking practices and the booking limit B is not observable. However, the prices p and ϕ are observable. 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 930 Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society The Customers: The total number of customers (i.e., market demand) is Λ ≥ 0. Here, Λ is a random variable with density g and distribution G; let ¼ 1 G. Each customer is a strategic utility maxiG mizer and makes two decisions sequentially: first, whether to make a reservation (paying the reservation fee), and second, whether to exercise the reservation (paying the service price) if one has been made. When making the former decision, customers are uncertain about how much value they will derive out of the firm’s service. This valuation u is independent and identically distributed across customers; it follows distribution F and density f, and let ¼ 1 F. Based on the distribution of valuations, F customers choose whether to make a reservation. If a customer chooses not to make a reservation, she leaves the market and receives zero utility. If a customer chooses to make a reservation, she faces the second decision, that is, whether to show up for the reservation and pay the price for service, after the service valuation u is realized. However, due to overbooking, it is possible that a reservation holder shows up for service while the firm does not have available capacity to serve the customer Figure 1. In this case, the customer incurs a denial cost c. We assume that the inconvenience of being bumped exceeds any potential compensation paid by the firm, so our analysis excludes customers who prefer to be bumped in hopes of earning the compensation, that is, c ≥ 0. Sequence of Events: The game chronology can be summarized as follows. First, the firm sets the reservation fee ϕ and the service price p, which are both publicly observable. In addition, the firm sets its booking limit B. Next, the market size Λ is realized; the firm observes the market size, but customers only know its distribution. Then, customers decide whether to make reservations and pay the reservation fee. The firm then accepts reservation requests up to the booking limit B. Finally, customers’ service valuations u are realized, and reservation holders decide whether to show up and pay the price of service. The firm serves customers up to Figure 1 Customers’ Decisions and Payoffs [Color figure can be viewed at wileyonlinelibrary.com] 931 its capacity limit μ. Figure 2 summarizes the sequence of events described above. The figure also labels the continuation equilibrium, which is the set of outcomes that follow a particular set of prices ϕ and p, and the full equilibrium, which consists of equilibrium prices and their corresponding continuation equilibrium. Utility Function: We now study customers’ utility function. Using backward induction, we first examine a reservation holder’s decision of whether to exercise the reservation (i.e., the second to last box in Figure 2). The decision depends on two factors: first, the customer’s valuation u, which has already been realized, and second, the customer’s probability q of receiving the service if she shows up. (We will derive q later in this section.) The customer’s expected utility is ðu pÞq cð1 qÞ ϕ, if show up, ϕ, if no show: Note that the customer pays the price of service p if service is rendered, but she incurs the denial cost c if capacity is unavailable despite securing the reservation; the former occurs with probability q. A reservation holder will thus show up when doing so yields a higher expected utility than not showing up and losing the reservation fee ϕ. In other words, to maximize expected utility, customers with realized 1q valuations u above the cutoff v ¼ p þ c q will show up, while other customers will not. Therefore, the expected utility from making a reservation is νðqÞ ¼ ϕ þ Eu maxfðu pÞq cð1 qÞ, 0g: When this expected utility is positive, customers will choose to make reservations. Profit Function: Next, we turn to the firm’s profit function in the continuation equilibrium. Having already chosen the prices ϕ and p, the firm is now choosing the booking limit B. We assume that customers make reservations; if they do not, the firm earns nothing and the booking limit plays no role. The firm’s expected profit as a function of the booking limit and customers’ cutoff valuation v is πðB; vÞ ¼ EΛ p min RðBÞ FðvÞ, μ þ ϕ RðBÞ C max RðBÞ FðvÞ μ, 0 , where R(B) ≡ min(B, Λ) is the number of reservations given out. There are three terms in the expectation. The first term is total revenue from service provision since a fraction FðvÞ of the R(B) reservation holders show up for service, and the firm may serve up to μ of them. The second term is the total 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Oh and Su: Optimal Pricing and Overbooking of Reservations Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society Figure 2 Sequence of Events [Color figure can be viewed at wileyonlinelibrary.com] revenue from reservation fees. The third term is the total bumping cost from turning away reservation holders. Based on this function, the firm chooses the optimal booking limit that maximizes the expected profit. Continuation Equilibrium: We are now ready to analyze the continuation equilibrium. Here, the prices ϕ and p have already been set. Based only on these prices, customers choose whether to make reservations. If they do not, the game ends and everyone earns nothing. In the more interesting case, customers make reservations, and the continuation equilibrium outcomes are described as what follows. DEFINITION 1. Given (ϕ, p), a continuation equilibrium ðBðϕ;pÞ , vðϕ;pÞ , qðϕ;pÞ Þ, in which customers make reservations, must satisfy the following conditions: (i) Bðϕ;pÞ ∈ arg maxB πðB; vðϕ;pÞ Þ, (ii) vðϕ;pÞ ¼ p þ c 1qðϕ;pÞ qðϕ;pÞ (iii) qðϕ;pÞ ¼ EΛ min , RðBðϕ;pÞ μ ÞFðv ðϕ;pÞ , 1 : Þ Condition (i) states that the booking limit Bðϕ;pÞ maximizes the firm’s expected profit, given the customers’ cutoff strategy vðϕ;pÞ . Condition (ii) states that the cutoff vðϕ;pÞ maximizes customers’ expected utility given the fill rate qðϕ;pÞ . Condition (iii) calculates the fill rate qðϕ;pÞ based on the firm’s and customers’ decisions Bðϕ;pÞ and vðϕ;pÞ . Together, these conditions characterize continuation equilibrium outcomes following prices ϕ and p, when customers make reservations. Full equilibrium: We are now ready to describe the full equilibrium of the game. Let π ðϕ, pÞ and ν ðϕ, pÞ, respectively, denote the firm’s expected profit and customers’ expected utility corresponding to the outcomes ðBðϕ;pÞ , vðϕ;pÞ , qðϕ;pÞ Þ described above. We have π ðϕ, pÞ ¼ πðBðϕ;pÞ ; vðϕ;pÞ Þ, ν ðϕ, pÞ ¼ νðqðϕ;pÞ Þ: A customer will make a reservation if the expected utility ν ðϕ, pÞ is greater than the outside option of zero. Therefore, the firm solves the following profit maximization problem: max ϕ, p π ðϕ, pÞ s:t: ν ðϕ, pÞ ≥ 0: The full equilibrium of the game is thus defined as follows. DEFINITION 2. The full equilibrium ðϕ , p , B , v , q Þ satisfies the following conditions. (i) (ii) (iii) (iv) ðϕ , p Þ ∈ arg maxðϕ;pÞ: ν ðϕ;pÞ≥0 π ðϕ, pÞ, B ¼ Bðϕ ; p Þ , v ¼ vðϕ ; p Þ , q ¼ qðϕ ; p Þ . Condition (i) requires that the firm’s pricing policy ðϕ , p Þ maximizes its expected profit in the continuation equilibrium while ensuring that customers are willing to make reservations. Conditions (ii), (iii), and (iv) ensure that ðB , v , q Þ is a continuation equilibrium given the prices ðϕ , p Þ. All our results below are based on analyses of the full equilibrium. 4. Analysis 4.1. The Overbooking Policy We begin by showing that there are two possible types of equilibria: the accept-all equilibrium and the booking-limit equilibrium. 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Oh and Su: Optimal Pricing and Overbooking of Reservations 932 Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society PROPOSITION 1. In the full equilibrium, ðB , v , q Þ must take one of the following two forms. (i) (Accept-all equilibrium) B ¼ ∞, v ¼ p þ c n o μ q ¼ EΛ min ΛFðv , 1 . Þ (ii) (Booking-limit q ¼ 1. equilibrium) μ B ¼ Fðp Þ, 1 q q , v ¼ p , In the first type of equilibrium shown in Proposition 1(i), the firm effectively accepts all reservation requests because the booking limit is B ¼ ∞. However, when market demand is too high, the firm does not have enough capacity to honor all the reservations it gives out. In other words, the probability that a reservation holder will be served is only q < 1. Customers anticipate this, so their cutoff valuation, 1 q v ¼ p þ c q , is strictly greater than the service price p to account for the risk of being bumped. We call this the accept-all equilibrium. In the second type of equilibrium shown in Propoμ sition 1(ii), the firm uses a booking limit B ¼ Fðp Þ. Specifically, the firm accepts up to B reservations, at which point it stops accepting any more that might be requested. The booking limit is chosen so that when it is reached, the expected number of reservation holders who show up for service is aligned with the units of capacity available. (Customers who realize that their valuation is below the price will not find it worthwhile to show up for service, so only a fraction Þ of reservation holders will show up.) Using the Fðp booking limit B , the firm ensures that all reservation holders who show up will be served in expectation (i.e., q ¼ 1). Consequently, the corresponding cutoff valuation v equals the service price p . We call this the booking-limit equilibrium. The two candidate equilibria reflect different priorities in reservation management. To explain this point, we present the following proposition. PROPOSITION 2. Consider some fixed (ϕ, p) with two continuation equilibria, one satisfying the conditions of the accept-all equilibrium and the other satisfying the conditions of the booking-limit equilibrium. Then, we have the following. (i) The accept-all equilibrium is more profitable if p is sufficiently small, but the booking-limit equilibrium is more profitable if p is sufficiently large. (ii) The accept-all equilibrium is more profitable if ϕ is sufficiently large, but the booking-limit equilibrium is more profitable if ϕ is sufficiently small. With two continuation equilibria following the same set of prices, a meaningful comparison between 933 the accept-all and the booking-limit reservation formats is possible. Note that the full equilibrium is uniquely determined since the firm chooses the format of continuation equilibrium that brings a higher expected profit. Even though these continuation equilibria may not occur in the full equilibrium, comparing them is instructive nonetheless. According to Proposition 2 above, if the firm relies heavily on reservation fees (i.e., high ϕ but low p), then the accept-all equilibrium is more profitable. This is reasonable since the accept-all equilibrium gives out more reservations and thus collects more reservation fees. On the other hand, if the firm relies more on the revenue collected from service, then the booking-limit equilibrium is more profitable. In this case, the booking limit helps to maintain high service levels, which supports higher service prices that contribute to higher revenue. Therefore, the two candidate equilibria reflect different priorities in reservation management: the accept-all equilibrium focuses on volume, while the booking-limit equilibrium focuses on service. We now study the market condition under which one equilibrium overbooking format outperforms the other. We focus on how market variability influences the optimal overbooking policy. In the following proposition, we assume that the market size Λ follows a normal distribution and study the effect of the standard deviation parameter, holding the mean fixed. PROPOSITION 3. Let market demand Λ follow a normal distribution Nðλ, σ 2 Þ truncated at zero. (i) If σ is sufficiently small, the equilibrium must be an accept-all equilibrium. (ii) If σ is sufficiently large, the equilibrium must be a booking-limit equilibrium. The result above shows that when the market variability is low, the firm accepts all reservation requests. The intuition is as follows. When market demand is relatively predictable, customers are in a good position to regulate their own arrival patterns and ensure that just the right amount of demand shows up for service. In the extreme case where demand is deterministic, customers can even ensure 100% service level by independently choosing whether to show up for service (cf. Lariviere and Van Mieghem 2004). For example, if everyone knows that there are 500 customers in the market and the firm has ample capacity to serve 400, an equilibrium will emerge whereby the 400 customers with the highest valuations will show up for service and all of them will be served. This outcome is possible because customers respond strategically to prices, that is, only customers with realized valuations above the service price will show up. Ultimately, it is the firm’s responsibility to set the right 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Oh and Su: Optimal Pricing and Overbooking of Reservations Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society service price so that just the right amount of demand shows up to fully utilize capacity. If the price is too high, too few customers show up and capacity is wasted; if the price is too low, too many show up and some of them are “bumped.” With the right prices, the accept-all equilibrium can indeed be optimal in predictable markets. On the other hand, when market variability is high, a booking limit must be used in equilibrium. This is because customers are no longer sufficiently wellinformed to regulate their own arrivals. Since customers are not privy to demand realizations, they decide whether to show up based only on their valuations. In equilibrium, the same proportion of reservation holders will show up for service, regardless of whether demand is high or low. To avoid having too many customers show up for service, a booking limit is needed. When demand is low, reservations can be given out without any restriction because the firm has ample capacity to honor them. However, when demand is high, the firm must limit the number of reservations in order to maintain reasonably high service levels. This role is served by the booking limit, which is necessary when the market variability is high. 4.2. The Pricing Policy In the previous section, we studied how booking limits can help firms hedge against the risk of bumping customers when the market size is uncertain. We now study how the firm can deal with customer valuation uncertainties using the reservation pricing policy. We begin by stating the following proposition, which shows the equilibrium pricing policies and their dependence on the average market size. To solicit the effect of the average market demand while keeping the analysis simple, we first study the case where the market size Λ is deterministic. PROPOSITION 4. When the market size Λ is deterministic, the equilibrium price ðϕ , p Þ satisfies the following. R∞ (i) If Λ ≤ μ: p ¼ 0 and ϕ ¼ 0 ufðuÞdu. R 1 ð μ Þ and ϕ ¼ ∞ ðu p ÞfðuÞdu. (ii) If Λ > μ: p ¼ F Λ p Therefore, the service price p increases as the market size Λ increases, and the reservation fee ϕ decreases and converges to zero as the market size Λ increases. Proposition 4(i) shows that when the market size is smaller than the capacity, the service price p becomes zero, so the firm’s revenue comes primarily from reservation fees. Since the bulk of the payment is received upfront, this scheme protects the firm against no-shows. In addition, this scheme leads to efficient consumption: since the firm essentially does not charge for service, all reservation holders with positive valuations will receive the service. In contrast, if the firm charges p > 0 for service, some customers with positive valuations below p will not show up, leading to lost surplus and hence lost profits (since the firm extracts full surplus). Therefore, the firm adopts a full prepayment scheme when average demand is sufficiently small. When the market size is larger than the capacity, on the other hand, Proposition 4(ii) shows that the firm charges service price so that customers can selfregulate to avoid being bumped. The fraction of customers having realized valuation greater than the price of service is set equal to the fraction of capacity over the market size. Hence, as the market size increases, the firm charges a higher service price p, but needs to correspondingly decrease the reservation fee ϕ to make reservations attractive ex ante. When the market size becomes significantly large, reservation fee ϕ becomes negligibly small, and reservations are offered for free. The results of Proposition 4 follow from the fact that the reservation price is paid before customers know their valuations, whereas the service price is paid after customers’ valuations are realized. When the firm is charging a price to customers who are unaware of their valuations, the firm can only set the price that is attractive to the customers in expectation. Therefore, the reservation deposit is set based on the customers’ expected valuation. In contrast, the service price that is charged after customers learn their valuations can actively depend on the market size. To illustrate, consider the case where a firm has 20 units of capacity to sell to the customers, and customers’ service valuations follow Uniform distribution with the support of [$0, $100]. If the firm sells the capacities to customers who have not yet seen their realized valuations, the only price the customers are willing to pay is less than or equal to their expected valuation of $50. However, if the firm sells the capacities to customers who already know their valuations, it can sell them to 20 customers who have the highest realized valuations. For example, if there are 100 customers in the potential market, the firm can sell its capacities to the top 20% of the population by setting the service price equal to $80. If there are 1000 customers in the potential market, the firm can now sell its capacities to top 2% of the population with the price of $98. As it can be seen in the above exercise, the market size does not have a direct effect on the prepaid reservation deposit, whereas the service price increases as the market size increases. When the firm charges both the reservation deposit and the service price as in our model, the firm increases the service price as the potential market size increases, and the prepayment needs to be lowered so that customers are willing to pay the deposit based on their expected utility. 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Oh and Su: Optimal Pricing and Overbooking of Reservations 934 Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society Proposition 4 also implies that the firm’s optimal pricing strategy for reservations diverges from the common belief that reservations are more useful when capacity is scarce. When the market size is large, this is when customers would value reservations more. However, our results show that the firm should give out reservations for free when the market size becomes significantly large. This is because customers view reservations as a means to secure capacity. However, to the firm reservations can be a tool to change the point of payment to maximize revenue. When the market size is small, the firm is better off charging the reservation deposit in advance while customers are still uncertain about their valuations. On the other hand, when there are more potential customers, the firm can sell its capacities at a higher price when the price is charged after customers find out their realized valuations. A key question in the advance selling literature is when one pricing scheme dominates the other between advance sales and spot sales. It is generally recognized that as the market size increases, the optimal policy switches from advance to spot sales (Xie and Shugan 2001). In comparison, with a generalization of advance selling in the form of reservations, we find that pure advance selling and pure spot selling are optimal only in extreme cases. In all other cases, it is important to consider a “hybrid” reservation system with two prices, ϕ and p. With two prices charged, we see that the market size has implications on pricing. Proposition 5 extends the results of Proposition 4 to the case where Λ is uncertain. PROPOSITION 5. Let λ = EΛ. (i) Suppose λ is sufficiently small such that the market demand Λ is smaller than μ with probability 1 − ɛ, for some small ɛ > 0. Then, p < ɛ. (ii) Suppose λ is sufficiently large such that the market demand Λ is greater than 1ɛ with probability 1 − ɛ, for some small ɛ > 0. Then, ϕ < ɛ. (iii) There is an increasing function p(λ) and a decreasing function ϕ(λ) such that for any λ, p ≥ pðλÞ and ϕ ≤ ϕðλÞ. Proposition 5 shows that (i) the service price p becomes negligible when the average market size is small, (ii) the reservation fee ϕ becomes negligibly small with a large enough market size, and (iii) the firm depends more heavily on the price of service and less so on the price of reservation as the market size increases. Our results are opposite from the findings of Georgiadis and Tang (2014), who find that prepayment plays a more important role in large rather than small 935 markets. The reason is as follows. In their model, the no-show probability is exogenous, so the number of reservation holders willing to show up cannot be manipulated using the service price. As market size increases, the opportunity cost of wasted capacity increases. Hence, it becomes more important to use prepayment to combat no-shows. In contrast, our model endogenizes customers’ decisions to show up for service. As market size increases, a greater number of reservation holders are willing to show up at each given price, so we can increase service price while fully utilizing capacity; the reservation fee correspondingly decreases. Consequently, there is less reliance on prepayment in larger markets. 4.3. The Overbooking and the Pricing Policies So far, we have seen how booking limits can be useful to deal with the market size uncertainty, while the pricing policy uses customer valuation uncertainty to maximize firm profit. As we studied the overbooking policy and the pricing policy separately, we showed how the format of the optimal overbooking policy depends on the standard deviation of the market size and how the pricing policy changes with the average market size. Now, to study how the mean and the standard deviation of the market size conjointly determine the optimal overbooking and the pricing policies, we run a numerical study using simulation method. While keeping the distribution of customer valuation as normal distribution with mean 200 and standard deviation 10, we vary the customers’ denial cost c and the firm’s bumping cost C where c = [50, 75, 100, . . ., 300] and C = [50, 75, 100, . . ., 300]. For each pair of c and C values, we vary the average market size/capacity ratio from 0.8 to 2 and the standard deviation of the market size from 0 to 100. We then compute the optimal pricing and the overbooking policy for each combination of mean market size/ capacity ratio and the standard deviation of market size. We first discuss the simulation results that show the market conditions that result in the accept-all equilibrium over the booking-limit equilibrium as shown in Figure 3. In Figure 3, the x-axis represents the values of average demand over capacity ranging from 0.8 to 2, whereas the y-axis shows the standard deviation of the market size ranging from 0 to 100. Figure 3 shows the results for the case where both the customers’ denial cost c and the firm’s bumping cost C are 100. The yellow squares represent the (average demand/capacity, standard deviation of market size) pairs that result in the accept-all equilibrium format, whereas the blue/green squares represent those pairs that result in the booking-limit equilibrium as the optimal overbooking policy. Among the squares that are of the booking-limit equilibrium, darker blue 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Oh and Su: Optimal Pricing and Overbooking of Reservations Oh and Su: Optimal Pricing and Overbooking of Reservations Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society Figure 3 Accept-all Equilibrium vs. Booking-limit Equilibrium. The Yellow Squares Represent the (average demand/capacity, standard deviation of market size) Pairs that Result in the Accept-all Equilibrium, Whereas the blue/green Squares Represent the Pairs that Result in the Booking-limit Equilibrium. Darker Blue Squares Represent Less Capacities being Overbooked; Squares that are Closer to Yellow in Color Represent Market Conditions Resulting in Larger Capacities being Overbooked [Color figure can be viewed at wileyonlinelibrary.com] squares represent the cases with less fraction of capacity being overbooked, whereas the squares that are closer to yellow in color represent booking limits that allow more capacity to be overbooked. From Figure 3 we confirm that the theoretical results of Proposition 3 hold: for a fixed value of average market size, the accept-all equilibrium is optimal when the standard deviation of the market size is small and the booking-limit equilibrium is optimal when the standard deviation of the market size is large. Figure 3 also shows that for a fixed value of market size standard deviation, the accept-all equilibrium is more profitable for smaller average market size values and the booking-limit equilibrium is more profitable for larger average market size values. From the above two facts, one can see that the threshold standard deviation of the market size below which the accept-all equilibrium is optimal decreases as the average market size increases. In other words, when the demand is low and/or predictable, the firm accepts all reservation requests, but when the demand is high and/or variable, the firm uses a booking limit. By the colors of Figure 3, one can also see that the fraction of capacity that is overbooked increases with average demand but decreases with the standard deviation of demand. From the simulation results, we can also see how the (average market size/capacity, standard deviation of the market size) pair affects the optimal reservation pricing policy as shown in Figure 4. Figure 4 shows how the fraction of the total payϕ ment paid as the reservation deposit, ϕ þ p, changes as the market condition changes for the case where both the customers’ denial cost c and the firm’s bumping cost C are 100. In Figure 4, the x-axes represent the values of average demand over capacity ranging from 0.8 to 2, and the y-axes represent the standard deviation of the market size ranging from 0 to 100. In Figure 4a, the height of each bar repreϕ sents the value of ϕ þ p for each pair of (average market size/capacity, standard deviation of market size). The yellow bars represent the cases where the firm only charges the reservation deposit with the service price of zero; the shorter the bars are, the smaller the fraction of the reservation deposit is in the total payment. Figure 4b shows the same information as Figure 4a but color codes the proportion of ϕ over the total payment on the two-dimensional market condition space. Each square represents an (average market size/capacity, standard deviation of market size) pair. The yellow squares show the market condition pairs that result in full prepayment as the optimal pricing policy. The darker blue squares represent the market conditions where the reservation deposits take smaller proportion of the total payment; the fraction of the prepayment becomes larger as the squares become closer to yellow in color. From Figure 4, we can confirm the results of Propositions 4 and 5. For a fixed value of market size standard deviation, the service price p equals zero for small markets so that the payment is purely made through the reservation deposit. As the average market size grows, the firm charges higher service price p, and the corresponding reservation deposit ϕ decreases. When the market size becomes significantly large, reservation deposit becomes negligible. By looking at Figures 3 and 4b together, we can infer how the overbooking policy and the reservation pricing policy interact as the market conditions change. As it was discussed following Propositions 3 and 4, when the market size is deterministic, the prices that maximize the profit can also regulate customer traffic perfectly and ensure 100% service level. However, as the market size variability increases, finding the profit-maximizing prices become a nontrivial task. In this case, optimal pricing policy alone becomes less competent in regulating customer traffic, and the firm needs a booking limit to avoid customer bumping. When the market size is highly variable, the actual market size can turn out to be quite different from the expected market size. Therefore, the firm should charge a non-negligible service price even in the case with small average market size keeping in mind that the market realization can be large. Likewise, the firm also has to charge a fair amount as the prepaid 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 936 Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society 937 Figure 4 Fraction of ϕ over ϕ + p [Color figure can be viewed at wileyonlinelibrary.com] ϕ Notes: (a) The height of each bar represents the value of ϕ þ p for each (average demand/capacity, standard deviation of market size) pair. (b) The yellow squares represent the (mean demand/capacity, standard deviation of market size) pairs that result in fully prepaid reservations; the green/blue squares represent the market condition pairs that result in partially prepaid reservations. The fraction of the prepayment becomes smaller as the squares become darker blue in color. 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Oh and Su: Optimal Pricing and Overbooking of Reservations Oh and Su: Optimal Pricing and Overbooking of Reservations Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society deposit even when the average market size is large knowing that the market can turn out to be smaller than expected. This can be seen from Figure 4b as the area of green squares become wider when the standard deviation of the market size grows. Note also that the (mean market size/capacity, standard deviation of market size) pairs that are lighter green in Figure 4b are in darker blue in Figure 3. This means that as it becomes a more challenging task to set the profit-maximizing prices, the firm tends to set more stringent booking limits to avoid the risk of bumping the customers. 5. Extension: Free Cancelation So far, we have studied how firms can set the optimal overbooking and pricing policies to deal with the uncertainties the firm and the customers face when reservations are made. We have studied how a firm can deal with the market size uncertainty by jointly utilizing the overbooking and the pricing policies. We have also looked at how the firm can resort to the pricing policies to manipulate the level of customer valuation uncertainty at the point payment takes place. In this section, we consider an extension of the base model where customers’ valuation uncertainties are resolved gradually over time. Through this extension, we intend to better understand how the firm’s pricing decision and its profitability depend on the point of sales as the customers’ level of knowledge on valuation changes over time. This extension also serves as a robustness check when richer customer choice dynamics are introduced. In our basic model, once customers book their reservations, their next decision was at the time of service when they either show up or not. However, during this interval, customers may learn more about their valuations and some may choose to cancel their reservations. This is a common occurrence, and it is useful to check the basic results in this scenario. The model is as what follows. In period 0, reservations are offered for free. In period 1, customers realize their types i ∈ {h, l}, where h represents the high type and l represents the low type. We assume that there are αΛ high type customers in the market, whereas the remaining (1− α)Λ are low type. Type-i customers have valuation for service ui , which is independent and identically distributed across the type-i customers; the valuation follows i ¼ 1 Fi . We distribution Fi and density f i with F assume that the high type customers’ valuation for service uh has first-order stochastic dominance over the low-type customers’ valuation ul so that for any l ðxÞ. Upon observing their types in h ðxÞ ≥ F given x, F period 1, customers decide whether they should keep their reservations or not. Customers who cancel their reservations need not pay anything, whereas those who decide to keep their reservations pay the price of reservation ϕ as was the case in the base model. In period 2, customers who have kept their reservations decide if they show up or not. A customer who shows up for her reservation and receives the service pays a price p; a customer who shows up but is denied a service incurs a cost c of being bumped. The firm then has two pricing strategies: (i) set (ϕ, p) so that both high type and low type customers keep their reservations in period 1, (ii) set (ϕ, p) so that only high type customers keep their reservations. Note that a strategy where only low type customers keeping their reservations is not feasible. We now state the equilibrium outcome as the following. PROPOSITION 6. In equilibrium, the followings are true. 1. When both types of customers keep reservations in period 1, ðB , v , q Þ must take one of the following two forms. (i) (Accept-all equilibrium) B ¼ ∞, v ¼ p þ 1 q μ c q , q ¼ EΛ min , 1 . l h αΛF ðv Þþð1αÞΛF ðv Þ (ii) (Booking-limit μ , h ðp Þ þ ð1 αÞF l ðp Þ αF equilibrium) v ¼ p , q ¼ 1. B ¼ 2. When only high type customers keep reservations in Step 1, ðB , v , q Þ must take one of the following two forms. (i) (Accept-all equilibrium) B ¼ ∞, v ¼ p þ μ c 1 q q , q ¼ EΛ min , 1 . h αΛF ðv Þ (ii) (Booking-limit equilibrium) B ¼ q ¼ 1. μ , h ðp Þ αF v ¼ p , From the above proposition, we show that there still exist two types of equilibria regarding the overbooking policy when customers are granted an option to cancel their reservations for free in advance. A natural question that follows then is when it is more profitable for the firm to set the prices (ϕ, p) so that low type customers take advantage of free cancelation. To simplify the analyses and focus on interesting findings, we assume that the market size Λ is deterministic for the rest of this section. PROPOSITION 7. such that ~ðΛÞ For a fixed constant Λ, there exists α ~ðΛÞ, both types of customers keep their 1. when α < α reservations in period 1, and 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 938 Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society 1 R ¼ Λ, p ≥ ðFÞ v ¼ p , q ¼ 1. μ Λ , ϕ ¼ R∞ p ðu p Þ f l ðuÞdu, ~ðΛÞ, only high type customers keep 2. when α ≥ α their reservations in period 1, and 1 h Þ μ , If αΛ ≥ μ, then R ¼ αΛ, p ¼ ðF Λ R∞ ϕ ¼ p ðu p Þ f h ðuÞdu, v ¼ p , q ¼ 1. R∞ If αΛ < μ, then R ¼ αΛ, p ¼ 0, ϕ ¼ p u f h ðuÞdu, v ¼ 0, q ¼ 1. Proposition 7(1) states that when the population of high type customers is not large enough, the firm should set the prices (ϕ, p) so that both types of customers keep their reservations. In this case, the prices are set to extract the surplus of low type customers while leaving positive surplus to high type customers. Proposition 7(2) states that when there are enough high type customers in the market, the firm should just have high type customers keep their reservations and low type customers cancel for free in period 1. By forgoing the profit from low type customers, the firm is able to charge prices (ϕ, p) so as to extract surplus from the high type customers. Note that in both cases of Proposition 7 we observe the pattern where the firm depends less on prepayment ϕ and more on the spot price p as the targeted market size grows. Another question of interest is if granting customers free cancelation is good for the firm, which is answered by the following proposition. PROPOSITION 8. For a fixed market size Λ, the following statements hold in equilibrium. ~ðΛÞ, offering free cancelation to customers 1. If α < α decreases the firm’s profit. ~ðΛÞ, offering free cancelation to customers 2. If α ≥ α increases the firm’s profit. Proposition 8(1) states that when there are not enough high type customers in the market and thus the firm sets the price so that both high type and low type customers keep their reservations in period 1, then the firm is better off not giving the option of free cancelation to the customers. This is because offering free cancelation allows low type customers to pay the price of reservation ϕ after they realize their types, whereas not offering free cancelation forces low type customers to pay the upfront reservation price when they are uncertain of their types. When customers are unsure of their types, they are willing to pay the reservation price based on their expected types; this price charged based on expectation is higher than the reservation price that can be charged to low type customers who are aware of their types. This shows that the result of Shugan and Xie (2005) where selling goods in 939 advance while customers are uncertain of their valuation bring higher profit to the seller extends to our case of two prices and two-stage realization of valuation. Proposition 8(2) conversely shows that when there are enough high type customers in the market and thus the firm sets the prices so that only high type customers keep their reservations, then the firm is better off by offering free cancelation to customers. This is because the firm now targets to sell reservations only to the high type customers with its increased price. Note that in Proposition 8(1) when offering free cancelation decreases firm’s profit, nobody exercises the option of free cancelation. On the other hand, when some customers indeed cancel their reservations for free, that is when offering free cancelation is more profitable to the firm as shown in Proposition 8(2). 6. Conclusion In this study, we study the optimal design of reservations. Our results provide two guiding principles for optimal reservation policies. • Principle 1: Reservations require a nonrefundable fee when booked and/or a service charge when used; the former dominates in small markets and the latter dominates in large markets. • Principle 2: All reservation requests can be accepted when demand is relatively low and/or predictable, but a booking limit is required to ensure that all reservations can be honored when demand is large and/or highly variable. These two principles characterize the optimal design of reservation dependent on market condition defined as a pair of mean and the standard deviation of market size. The reasoning behind our principles can be outlined as follows. The first principle holds because reservation holders consider prices when choosing whether to show up for service. Firms facing low demand should charge low service prices and high reservation deposit since they can sell their capacities at a higher price when customers make the payments in advance without knowing their valuations for service. On the other hand, firms facing high demand do not rely on the nonrefundable deposit because they can charge high service prices: even when the service price is high, there is sufficient demand to fully utilize capacity. This logic brings us to the second principle. When aggregate demand is publicly known, all reservations can be accepted because the fixed market of customers respond to prices and show up in the appropriate numbers. However, in unpredictable markets, customers do not know the realized number 19375956, 2022, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/poms.13583 by Vrije Universiteit Amsterdam, Wiley Online Library on [07/03/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Oh and Su: Optimal Pricing and Overbooking of Reservations Oh and Su: Optimal Pricing and Overbooking of Reservations Production and Operations Management 31(3), pp. 928–940, © 2021 Production and Operations Management Society of reservation requests and too many may show up; in such cases, a booking limit helps ensure that not too many reservations are given out so they can all be fulfilled. The current work can be extended in three broad directions. First, we have not examined the role of competition. When there are multiple firms, price competition becomes an issue, and moreover, the possibility that customers may take reservations from multiple firms complicates overbooking decisions. 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