A contract is a legal agreement and key factor in implementation of tasks within system engineering management as well as in the ensuring of system performance within acquistion management phases. First, we survey and describe current contract types. From the client's perspective, we then take into account such criteria as the bidder's quality reputation and technical advantage. Further, we apply the specific structural property from the Analytic Hierarchy Process to build the most appropriate contractor evaluation model. Finally, fighter aircraft performance enhancement is given as an example to illustrate the applicability of our model. In order to deal with project variables and contingencies within contract execution, the sequential decisions property of the Decision Tree Analysis is used to assist c1ients in selecting suitable contract types. By so doing, we demonstrate the contract decision processes.