Common use of Onerous Clause in Contracts

Onerous. Aleatory contract: one of the parties or both reciprocally bind themselves to give or to do something in consideration of what the other shall give or do upon the happening of an event which is uncertain, or which is to occur at an indeterminate time. (Ex: Sale of sweepstakes ticket)  exclusive right and privilege to purchase an object.  a bilateral contract whereby the prospective seller, while expressly reserving the ownership of the subject property despite delivery thereof to the prospective buyer binds himself to sell the said property exclusively to the prospective buyer upon fulfilment of the condition agreed upon, that is, full payment of the purchase price.