Sea Foam Motor Treatment is made from petroleum, just like gasoline, diesel and motor oils. When added to petroleum fuel, Sea Foam’s ingredients immediately disburse evenly into the total volume of gas in the tank. As far was the best time to add, you can add when the tank is low or when it’s full. Just know that the more Sea Foam you add to a low amount of fuel, the greater the cleaning concentration. A lot of people like to add a full can or two when the tank is low, drive 20 to 50 miles, then add more fuel.