The most common type of Islamic trade where the selling price of a commodity is negotiated between the seller and the buyer, with the cost price being unknown to the latter. Following Shari'ah law, there are restrictions for this kind of trade to exist. Firstly, the product or services being traded need to be wholly owned by the seller. Secondly, the sale must take place at the time the product or service is being traded, not at any future time, and lastly, the product or service must be valuable and usable.