gasoline is sold at gas stations (petrol stations). in order to burn properly in high-compression internal combustion engines, each brand of gasoline includes gasoline additives. so, the exact make up of gasoline is different at different stations. gasoline is graded by its octane rating that measures how well it will burn. most car engines can burn "regular" gasoline which has an octane rating of 87. precision-made engines require or prefer "premium" gasoline with an octane rating of 93. most stations offer three different mixtures of gasoline with three separate octane ratings and prices.