Offer and acceptance

Offer and acceptance are generally recognized as essential requirements for the formation of a contract (together with other requirements such as consideration and legal capacity). Analysis of their operation is a traditional approach in contract law. This classical approach to contract formation has been modified by developments in the law of estoppel, misleading conduct, misrepresentation, unjust enrichment, and power of acceptance.

Treitel defines an offer as "an expression of willingness to contract on certain terms, made with the intention that it shall become binding as soon as it is accepted by the person to whom it is addressed", the "offeree". An offer is a statement of the terms on which the offeror is willing to be bound.

The expression of an offer may take different forms, and which form is acceptable varies by jurisdiction. Offers may be presented in a letter, newspaper advertisement, fax, email verbally or even conduct, as long as it communicates the basis on which the offeror is prepared to contract. Traditionally the common law treated advertisements as being unable to contain offers, but that view is less forceful in jurisdictions today.

Whether the two parties have reached agreement on the terms or whether a valid offer has been made is a legal question. In some jurisdictions, courts use criteria known as 'the objective test', which was explained in the leading English case of Smith v. Hughes. In Smith v. Hughes, the court emphasised that the important thing in determining whether there has been a valid offer is not the party's own (subjective) intentions but how a reasonable person would view the situation. The objective test has largely been superseded in the UK by the introduction of the Brussels Regime in combination with the Rome I Regulation.

An offer can be the basis of a binding contract only if it contains the key terms of the contract. For example, in some jurisdictions, a minimum requirement for sale of goods contracts is the following four terms: delivery date, price, terms of payment that includes the date of payment, and a detailed description of the item on offer including a fair description of the condition or type of service. Other jurisdictions vary or eliminate these requirements. Unless the minimum requirements are met, an offer of sale is not classified by the courts as a legal offer but is instead seen as an advertisement.

In line with the definition from Treitel above, to invite acceptance an offer must be serious. In this sense, an obvious joke cannot become the basis of an offer because the potential offeror lacks actual intent to enter into an exchange. For instance, in the famous case of Leonard v. Pepsico, Inc., depiction of a military aircraft offered in exchange for "Pepsi Points" was interpreted by a court as a joke. Despite having clear terms (7,000,000 Pepsi Points in exchange for one aircraft), the humorous elements of the commercial rendered that portion of the advertisement a joke rather than a serious offer.

Whether a potential offer is serious is evaluated under an objective standard, independent of the subjective intent of the one making or accepting the offer. In the case of Lucy v. Zehmer, what one party believed were jests about selling a farm turned into a binding contract, based on the court's evaluation of the circumstance from the perspective of a reasonable observer. Similarly, in the case of Berry v. Gulf Coast Wings Inc., one party's offer of a "Toyota" for the winner of a contest was interpreted as requiring the offeror to provide a vehicle to the winner rather than a "Toy Yoda" doll from Star Wars, despite the assertion that the contest was based on a joke.

A unilateral contract is created when someone offers to do something "in return for" the performance of the act stipulated in the offer. In a unilateral contract, acceptance may not have to be communicated and can be accepted through conduct by performing the act. Nonetheless, the person performing the act must do it in reliance on the offer.