There is no real good reason for this I am sure that the people who own gas stations do not have to buy new gas every day.
The good practice would be to take the price of the gas they bought, add their proportional business cost and their margin and set that price until the next time they buy gas.
What they really do is look at what other gas stations prices and set a similar price - high enough to make a bargain but low enough to not scare any customers away.
Because the price of gasoline is influenced by a global market called Oil or Petroleum. The whole economy fluctuates daily and people are making tons on money off of it with stocks, bonds, dividends, and margins. When people sell stock in oil it causes the prices of its related products to go down due to less demand. When people are buying Oil again the prices go back up as supply diminishes with more demand... It's very detailed and complicated lol.
Rules of supply and demand, the price fluxuation of crude oil per barrel and it's mostly controlled by the stock market.
Dunno but its very annoying
haha i know