The term “unilateral contract” refers to a contract whereby one party makes an express engagement or undertakes a performance, without receiving in return any express engagement or promise of performance from the other.

Davis v. Jacoby, 1 Cal. 2d 370 (1934).

The distinction between unilateral and bilateral contracts is well settled in the law. It is well stated in section 12 of the American Institute’s Restatement of the Law of Contracts as follows:

“A unilateral contract is one in which no promisor receives a promise as consideration for his promise. A bilateral contract is one in which there are mutual promises between two parties to the contract; each party being both a promisor and a promisee.”

In the case of unilateral contracts no notice of acceptance by performance is required. Section 1584 of the Civil Code provides, “Performance of the conditions of a proposal, … is an acceptance of the proposal.”

Although the legal distinction between unilateral and bilateral contracts is thus well settled, the difficulty in any particular case is to determine whether the particular offer is one to enter into a bilateral or unilateral contract. Some cases are quite clear cut. Thus an offer to sell which is accepted is clearly a bilateral contract, while an offer of a reward is a clear-cut offer of a unilateral contract which cannot be accepted by a promise to perform, but only by performance.  Between these two extremes is a vague field where the particular contract may be unilateral or bilateral depending upon the intent of the offerer and the facts and circumstances of each case. The offer to contract involved in this case falls within this category. By the provisions of the Restatement of the Law of Contracts it is expressly provided that there is a presumption that the offer is to enter into a bilateral contract. Section 31 provides:

“In case of doubt it is presumed that an offer invites the formation of a bilateral contract by an acceptance amounting in effect to a promise by the offeree to perform what the offer requests, rather than the formation of one or more unilateral contracts by actual performance on the part of the offeree.”

Professor Williston in his Treatise on Contracts, volume 1, section 60, also takes the position that a presumption in favor of bilateral contracts exists.

In the comment following section 31 of the Restatement the reason for such presumption is stated as follows:

“It is not always easy to determine whether an offerer requests an act or a promise to do the act. As a bilateral contract immediately and fully protects both parties, the interpretation is favored that a bilateral contract is proposed.”

While the California cases have never expressly held that a presumption in favor of bilateral contracts exists, the cases clearly indicate a tendency to treat offers as offers of bilateral rather than of unilateral contracts.