The minimum variance hedge ratio, also known as the optimal hedge ratio, is a formula to evaluate the correlation between the variance in the value of an asset or liability and that of the hedging instrument that is meant to protect it. The minimum variance ratio is used by businesses and investors who hedge their exposure with futures contracts. Since perfect hedging does not exist, in some cases treasurers need to calculate the minimum variance hedge ratio to find out the suboptimal number of contracts in order to offset their exposure to the potential changes in the value of their underlying asset or liability. A typical example of this is an airline who, because their business is exposed to variations in fuel prices, might want to protect their margins with futures contracts. As there is no jet fuel futures market, the company will have to look for suboptimal contracts, that is, the futures contracts with the highest correlation with the underlying asset – in this case, jet fuel.