The oil-storage trade is a trading strategy where oil tank owners and companies that lease storage buy oil for immediate delivery and hold it in their storage tanks, then sell contracts for future delivery at a higher price. When delivery dates approach, they close out existing contracts and sell new ones for future delivery of the same oil. The oil never moves out of storage. Trading in this fashion is only successful if the forward market is in "contango", that is if the price of oil in the future also known as forward prices are higher than current prices or spot prices. The concept was introduced on the market in early 1990 by the Scandinavian Tank Storage company, Scandinavian Tank Storage AB and its founder Lars Jacobsson.
Storing oil became big business in 2008 and 2009, with many participants—including Wall Street giants, such as Morgan Stanley, Goldman Sachs, and Citicorp—turning sizeable profits simply by sitting on tanks of oil. Institutional investors bet on the future of oil prices through a financial instrument, oil futures in which they agree on a contract basis, to buy or sell oil at a set date in the future. Investors can choose to take profits or losses prior to the oil-delivery date arrives. Or they can leave the contract in place and physical oil is "delivered on the set date" to an "officially designated delivery point", in the United States, that is usually Cushing, Oklahoma. By May, 2007 Cushing's inventory fell by nearly 35% as the oil-storage trade heated up.
According to Steve Christy researcher with Gibson Shipbrokers in London, a specialist in tanker markets, at the end of October, 2009, one in twelve of the largest oil tankers were being used more for temporary storage of oil, rather than transportation.; and that if lined up end to end, the tankers would stretch out for 26 miles. "The trend follows a spike in oil futures prices that has created incentives for traders to buy crude oil and oil products at current rates, sell them on futures markets and store them until delivery." 
- Norris, Michele (17 December 2008). "Contango In Oil Markets Explained".
- Davis, Anne (6 October 2007). "Where Has All The Oil Gone? After Sitting on Crude, Speculators Unload It. The World's Eyes Fall on Cushing, Oklahoma". Wall Street Journal.
- Wright, Robert (17 November 2009). "Tankers store oil as futures prices rocket". Financial Times. London, UK.