A lot of folks believe that the big oil companies manipulate the price of gasoline by, for example, taking refinery capacity off-line for maintenance in the middle of the summer or failing to invest in sufficient refinery capacity to meet demand.

From a posting in today's Slashdot comes one that would not have occurred to me: That gasoline prices are calibrated based on 60F temperatures but that in many states the gasoline is sold at higher temperatures.

The SlashDot article suggests that the oil companies, by refusing to account for the changing density of the gasoline as temperatures rise, are manipulating consumers. Since gasoline expands as it warms, consumers receive less energy per gallon when they purchase warm gasoline than they would if the gasoline they purchased were colder.

Most gasoline is stored in underground storage tanks where it is relatively unaffected by the heat of the day---still, some gas is stored in the pump itself, so gas purchased in the cool of the morning is, at least fractionally, cheaper than gas purchased at high noon of a hot day.