Adding oil to your fuel is essential to keep your engine running smoothly. However, knowing when and how much oil to add can be challenging. Here are a few tips to help you out: If you have a two-stroke engine, mix the fuel and oil yourself. Some owners prefer making their fuel because they want more control over what they do with it. The amount of oil to use depends on the size of your boat and your personal preference. It’s essential to know how much oil you need in the fuel. If your boat engine requires a specific ratio of oil in the fuel, it’s necessary to purchase accordingly. Trying to calculate the amount at the pump can slow you down, so many people prefer pre-mixing your fuel. Two-stroke engines require a 100:1 ratio, but some think a 50:1 balance is better for them. For the primary 50:1 ratio, you will need 2.6 fluid ounces of oil per gallon of gas added.