本文利用或有求償權分析法探討：單期、兩期、及一般化的多期合理訂金水準， 並討論多期訂金繳交過程中的「斷頭價格」。就多期訂金而言，隨著訂金繳款期數的增加， 其所對應每一期所需繳付的訂金水準隨之降低，可是所收取的訂金總額卻隨之增高；而就不 同期中繳款日之最適斷頭價格而言，則是隨著時間經過而降低並向尾款趨近。最後本文亦探 討，允許賣方違約，但必須支付違約金之合理訂金水準。

　　　　　This paper values the deposit of purchase contract in a contingent claim framework. Based on the theoretical model, we examine the one-period, two-period and multi-period models to evaluate the fair deposit of the contract. We also discuss the buyer's threshold price in two-period and multi-period contracts under the concept of compound option. Finally, we consider the default possibility of sellers with the fair deposit.