No, although it is advisable to stick to our guidelines in order to not needlessly waste money on excess Oxytane. The mixing ratio is 5000:1 (Fuel to Oxytane). This means that 10ml of Oxytane will treat 50L of fuel (Approx 1 full tank of fuel on a small or medium sized car). 20ml will treat 100L of fuel, which is perfect for 1 full tank on a larger car, pick-up truck of van.