Which type of contract allows each party to obtain an advantage in exchange for their obligations?

The correct choice is onerous. In the context of contracts, an onerous contract is characterized by an exchange of benefits and burdens between the parties involved. Each party agrees to perform certain duties or obligations, and in return, they receive a corresponding advantage or benefit. This mutual exchange is essential to the nature of an onerous contract, as it means that both parties are bound by their commitments and expect to gain something of value from the agreement.

In contrast, unilateral contracts involve only one party making a promise or commitment without requiring reciprocal performance or obligation from the other party. Gratuitous contracts, on the other hand, involve no exchange of consideration—one party provides a benefit without expecting anything in return. Aleatory contracts incorporate elements of chance, where the performance of an obligation depends on the occurrence of a specific uncertain event. Given these distinctions, the onerous contract clearly emphasizes the mutual exchange of benefits, making it the correct answer in this context.