My impression of the gasoline industry is that there is 1) a wholesale price paid to refiners by gas stations who receive large shipments of gasoline in tanker trucks on (roughly) a daily basis, and 2) a retail price for customers set by individual gas stations, which can change multiple times per day. Some people get upset at mid-day changes in the retail price, arguing that all gasoline purchased from a tanker truck early in the morning at a particular wholesale price should be sold at the same retail price throughout the day (i.e., there should be a constant mark-up over the wholesale price). What defense could be given to support the phenomenon of changing retail prices throughout the day, even if the earlier wholesale price has not changed?