In a unilateral contract, which party's promise is considered enforceable?

In a unilateral contract, the enforceability is centered around the promise made by only one party. In the context of insurance, particularly surplus lines, this means that the insurer makes a promise to provide coverage in exchange for the insured's payment of the premium. The insurer is obligated to fulfill their promise, while the insured’s promise to pay the premium is not enforceable until they actually make that payment.

This characteristic of unilateral contracts distinguishes them from bilateral contracts, where both parties have enforceable promises. In the case of a typical insurance policy, the insured has the option to pay for the coverage but is not required to do so until they choose to accept the terms of the policy, therefore the enforceability lies exclusively with the insurer's promise to provide coverage.