Contango is a situation in which the futures price (or forward price) of a commodity is higher than the spot price. In a contango situation, arbitrageurs or speculators are "willing to pay more for a commodity [to be received] at some point in the future than to purchase the commodity immediately. This may be due to people's desire to pay a premium to have the commodity in the future rather than paying the costs of storage and carry costs of buying the commodity today."

On the other side of the trade, hedgers (commodity producers and commodity holders) are happy to sell futures contracts and accept the higher-than-expected returns. A contango market is also known as a normal market or carrying-cost market.

The opposite market condition to contango is known as backwardation. "A market is 'in backwardation' when the futures price is below the spot price for a particular commodity. This is favorable for investors who have long positions since they want the futures price to rise to the level of the current spot price".

In industry parlance, contango may refer to the situation when futures prices (or forward prices) are above the current spot price, or a far-dated futures price is above a near-dated futures price, and the expectation is for the spot price to rise to the futures price at maturity, or the near-dated futures price to rise to the far-dated futures price.

The Commission of the European Communities, in a report on agricultural commodity speculation, defined backwardation and contango in relation to spot prices: "The futures price may be either higher or lower than the spot price. When the spot price is higher than the futures price, the market is said to be in backwardation. It is often called 'normal backwardation' as the futures buyer is rewarded for risk he takes off the producer. If the spot price is lower than the futures price, the market is in contango".

A normal forward curve depicting the prices of multiple contracts, all for the same good, but of different maturities, slopes upward. For example, a forward oil contract for twelve months in the future is selling for $100 today, while today's spot price is $75. The expected spot price twelve months in the future may actually still be $75. To purchase a contract at more than $75 supposes a loss (the "loss" would be $25 if the contract were purchased for $100) to the agent who "bought forward" as opposed to waiting a year to buy at the spot price when oil is actually needed.

But even so, there is utility for the forward buyer in the deal.

Experience tells major end users of commodities (such as gasoline refiners, or cereal companies that use great quantities of grain) that spot prices are unpredictable. Locking in a future price puts the purchaser "first in line" for delivery even though the contract will, as it matures, converge on the spot price as shown in the graph. In uncertain markets where end users must constantly have a certain input of a stock of goods, a combination of forward (future) and spot buying reduces uncertainty.

An oil refiner might purchase 50% spot and 50% forward, getting an averaged price of $87.50 for the one barrel spot ($75) and the one barrel bought forward ($100).

If short-term interest rates were expected to fall in a contango market, this would narrow the spread between a futures contract and an underlying asset in good supply. This is because the cost of carry will fall due to the lower interest rate, which in turn results in the difference between the price of the future and the underlying growing smaller (i.e. narrowing). An investor would be advised to buy the spread in these circumstances: this is a calendar spread trade where the trader buys the near-dated instrument and simultaneously sells the far-dated instrument (i.e. the future).

If, on the other hand, the spread between a future traded on an underlying asset and the spot price of the underlying asset was set to widen, possibly due to a rise in short-term interest rates, then an investor would be advised to sell the spread (i.e. a calendar spread where the trader sells the near-dated instrument and simultaneously buys the future on the underlying).

In a 2010 article in Harper's Magazine, Frederick Kaufman argued the Goldman Sachs Commodity Index caused a demand shock in wheat and a contango market on the Chicago Mercantile Exchange, contributing to the 2007–2008 world food price crisis.

In a June 2010 article in The Economist, the argument is made that index-tracking funds (to which Goldman Sachs Commodity Index was linked) did not cause the bubble. It describes a report by the Organisation for Economic Co-operation and Development that used data from the Commodity Futures Trading Commission to make the case.

The term originated in 19th century England and is believed to be a corruption of "continuation", "continue" or "contingent". In the past on the London Stock Exchange, contango was a fee paid by a buyer to a seller when the buyer wished to defer settlement of the trade they had agreed. The charge was based on the interest forgone by the seller not being paid.

The purpose was normally speculative. Settlement days were on a fixed schedule (such as fortnightly) and a speculative buyer did not have to take delivery and pay for stock until the following settlement day, and on that day could "carry over" their position to the next by paying the contango fee. This practice was common before 1930, but came to be used less and less, particularly after options were reintroduced in 1958.

This fee was similar in character to the present meaning of contango, i.e., future delivery costing more than immediate delivery, and the charge representing cost of carry to the holder.