The opposite market condition to contango is known as backwardation. The opposite market condition to normal backwardation is known as contango. Economic theory regarding backwardation and contango is associated with John Maynard Keynes and John Hicks. July tomatoes are effectively a different commodity from January tomatoes (contrast contango and backwardation). Likewise, contango implies that futures prices for a certain maturity are falling over time. In this situation, called contango, speculators must be net short. For perishable commodities, price differences between near and far delivery are not a contango. A contango is normal for a non-perishable commodity that has a cost of carry. A contango market is also known as a normal market, or carrying-cost market. Speculation and investment requirements later shaped the common contango trend. The opposite situation, where formula 36, is referred to as contango. Contango is a potential trap for unwary investors. This situation is an extreme case of contango. Contango used to be the 'normal' for the oil market.