A random contract (from the Latin alea, "luck") is that type of bilateral legal act, of an onerous nature, in which it is agreed that one of the benefits due is subject, in terms of the possibility, quantity or quality of the benefit, to what could occur in the future, without this event being qualified as a condition "Condition (Right)") of the contract (since the contract exists independently of the event), but rather as a contingency of profit or loss.

This is defined, among others, by art. 1790 of the Spanish Civil Code:.

Meanwhile, the Chilean Civil Code establishes in its art. 1441:.

Legislation tends to agree on the following examples of random contracts: