Prices accross the street depend on what time of the day it is, where in the city you are, and how much the owner of the store paid for the gas in the first place. Usually, the further away you get from a highway the cheaper it will be. And gas is usually more expensive during the day than it is at night. And I've heard that the price on the sign and on the pump are for cash only. You actually pay a little more if you use a card. Different companies will also add different types and amounts of additives, which will make for more expensive fuel.