Lucas recommends using their fuel injector cleaner as follows: The recommended dosage is 2-3 ounces of Fuel Treatment for every 10 gallons of gasoline or diesel fuel. Pour Lucas Fuel Treatment directly into the fuel tank. Exceeding the recommended dosage is not harmful to your vehicle. As a guideline, their products should last: 5.25oz Bottle - One bottle treats up to 25 gallons of fuel. 1 Quart/32oz Bottle - One bottle treats up to 100 gallons of fuel. 1 Gallon/128oz Bottle - One bottle treats up to 400 gallons of fuel.