what is the correlation between temperature and gas mileage?

Answer 1

The vapor from gasoline products are what allow for internal combustion to take place in car engines. The warmer the temperature, the more vapor is created (fuel is burned off more quickly). That is why, during the summer months, fuel terminals convert from a high RVP (Reid Vapor Pressure) fuel, to a lower RVP -- a conversion that, in part, causes the gas prices to go up.

Answer 2

Gasoline is measured by volue when you buy it. In the summer time when the gasoline is warm you do not get as much mass in tank when you buy a certain volume of gas as when it is cold.