That price would be per liter; they use the metric system
Now imagine filling up your gas tank by typical 2 liter plastic bottles.
An imperial gallon of liquid is defined as 4.54609 litres,
Now multiply that $1.38 by 4.54609 and you have your answer !
The U.S. Gallon is 3.78541 liters, the U.S. dollar is 1.38 AU dollars, you are using a bigger gallon and smaller dollar. Price is $3.81/GAL is U.S. dollars and gallons.