According to the FTC study, when gas prices go down,

Gasoline retail prices rise four times faster than they fall after the wholesale price changes, according to a Federal Trade Commission(FTC)study. In some places around the country, gasoline retailers sell at a loss when wholesale prices are high, and they try to make up that loss when prices go down, said Matthew Chesnes, the economist who conducted the FTC study. Gas stations make most of their profit from attached convenience stores.(6)If a sign boasting low prices draws drivers to the station, they’re more likely to spend money in the store. The competition usually isn’t as cutthroat on the way down as it is on the way up, Chesnes said. Some research suggests that when prices are high, buyers search around to find a better deal. Immediately after prices go down, though, buyers don’t search as hard. This gives a cushion for the station owners to lower prices in smaller increments.