Which type of contract involves unequal value exchanges that depend on uncertain events?

The correct answer is aleatory contract. This type of contract is characterized by the fact that the exchange of value between the parties depends on the occurrence of uncertain events. In an aleatory contract, one party may receive a benefit that is significantly greater than what they paid, while the other party assumes a risk that may or may not pay off. A common example of this is insurance contracts, where the insurer pays a claim based on an event occurring, which is uncertain and may be infrequent.

A unilateral contract involves a promise made by one party in exchange for an action by another; this does not inherently depend on an uncertain event in the same way an aleatory contract does. An adhesion contract is typically a standard form contract drafted by one party, leaving the other with little room for negotiation; this type of contract does not directly relate to the concept of unequal value based on uncertain events. An express contract, on the other hand, is one where the terms are clearly stated and agreed upon, not relying on uncertainty in value exchanges. These distinctions highlight why the aleatory contract is the most fitting choice for the described scenario.