248 N.Y. 86, 161 N.E. 428 (N.Y. 1928)
Petterson v. Pattberg is a staple of first-year Contracts because it crystallizes the classical common-law view of unilateral contracts: an offer inviting acceptance only by performance may be revoked at any time before that performance is fully completed.
When an offer invites acceptance only by performance (a unilateral offer), may the offeror revoke the offer before the offeree completes the requested act, and does a refused tender constitute acceptance sufficient to form a contract obligating the offeror?
Under the classical unilateral contract doctrine, an offer that invites acceptance solely by performance may be revoked at any time prior to the offeree's complete performance, absent an enforceable option supported by consideration or other binding irrevocability. Acceptance of such an offer requires actual completion of the requested act; a mere tender or statement of readiness, if refused by the offeror, does not consummate acceptance. Performance of a preexisting duty owed to the offeror does not furnish consideration for an option to keep the offer open.
No contract was formed. Pattberg effectively revoked his unilateral offer before Petterson completed performance; Petterson's refused tender did not constitute acceptance, and no consideration supported any option to keep the offer open. The Court of Appeals reversed and dismissed the complaint.
Petterson v. Pattberg is a canonical exposition of the classical unilateral contract rule and remains a teaching vehicle for three core concepts: acceptance by performance, revocation before acceptance, and the limits of tender when the offer invites only performance. Its perceived harshness spurred doctrinal evolution; the Restatement (Second) of Contracts § 45 now provides that the beginning of invited performance creates an option contract rendering the offer temporarily irrevocable. The case thus anchors exam analysis of unilateral offers and highlights the contrast between classical formalism and modern protection of reliance and partial performance.