A distinction is usually made between advertisements for a unilateral and bilateral contract. An advertisement is a notice or an announcement in a public medium promoting a product, service, event, or publicizing a job vacancy.
Advertisements for unilateral contracts
These include advertisements offering rewards for the return of lost property or for information leading to the arrest or conviction of a criminal. Such advertisements are usually treated as offers, on the basis that the contract can normally be accepted without any need for further negotiations between the parties, and the person making the advertisement intends to be bound by it. This is the position in the cases of Carlill v Carbolic Smoke Ball Co. and Lefkowitz v Great Minneapolis Surplus Store 1957.
Advertisement for a bilateral contract
These are the types that advertise specified goods at a certain price, such as those found in shop windows and on the classified pages of newspapers and magazines. They are usually considered an invitation to treat on grounds that they lead to further bargaining as potential buyers may want to negotiate about the price. In Grainger & Sons v Gough (1986) it was held that the circulation of a price list by a wine merchant was not an offer to buy at those prices but merely an invitation to treat.