Being clear is one of the validity conditions of the sale contract. However, in some contracts particularly contracts related to the energy sector the price is not specify in detailed at time of the conclusion of contract. Such contracts is titled the sale by open price. In such contracts, the parties cannot or will not specify the price exactly at time of conclusion but they are assigned the determination of price to indicators more or less variable in future and even in some cases lay dormant. Because of growing volume of these contracts studying their legal status is necessary. The question of this paper is that whether sale by open price is valid because of the pretext of nullity of the contract and defects in the conditions of the contract? This paper is to studying the principles of issue in Jurisprudence and Iranian law is pave the way for the acceptance and development of such contracts.