What is the ruling on buying olive oil and paying its price before it is harvested?

If the sale is in the form of a salam (forward) contract, then there is no legal impediment to it. The conditions for this are that the capital must be paid in full at the time of the contract, and it must not be stipulated that the olive oil comes from a specific farm, because there is no guarantee against its spoilage. However, if the sale is not in the form of a salam contract, then it is impermissible due to the elements of jahalah (uncertainty), gharar (excessive risk), and selling what the seller does not possess.