Bilateral contracts are also classified into two groups: Equal bilateral contracts and unequal bilateral contracts. In equal bilateral contracts,there are mutual promises between the two parties and they involve an exchange of equivalent mutual obligations. Examples to equal bilateral contracts are sales contract, rental contract and employment contract. On the other hand, in unequal bilateral contracts, the parties are both under an obligation, but their obligation is not mutual, and in other words one obligation is not exchanged for theother. Contract of agency and loan contracts can be given as examples.