Gas prices in the U.S. are given by the gallon; to convert them to liters, you'll divide the price by the number of liters in a gallon, 3.78541. So if gas costs $3.50 per gallon, you have $3.50 ÷ 3.78541 = $0.92460 per liter, which would typically be rounded to $0.92 per liter.
