Which type of contract places an obligation only on one party?

A unilateral contract places an obligation solely on one party. In this type of agreement, one party makes a promise in exchange for an act performed by the other party. The classic example is a reward contract, where one party offers a reward for the performance of a specific task, such as finding a lost pet. In this case, only the party offering the reward has a contractual obligation, and the other party only accepts the contract by completing the act.

Bilateral contracts, on the other hand, involve mutual obligations where both parties make promises to each other. An implied contract arises from actions or behavior rather than explicit agreements, while a counteroffer represents a response to an initial offer, introducing new terms and thereby negating the original offer. Thus, these types do not satisfy the requirement of having an obligation placed only on one party.