A unilateral contract is a contract by which there is a commitment to pay or provide another consideration in exchange for the actual benefit. (I`ll pay you $500 to repair my car by Thursday; the power is repairing the car until that date). A bilateral treaty is a treaty that trades a promise for a promise. (I promise to fix your car by Thursday and promise to pay $500 on Thursday). Contracts can be written or orally, but oral contracts are more difficult to prove and in most jurisdictions the time against the contract is shorter (for example. B two years for oral versus four years for written writing).