You can buy pur csator oil from wal mart in 4 oz bottles for about 2 bucks each. I usually add 8ozs of casor oil to every gallon of fuel. Sure its a little messier but i dont mind cleaning up the mess. The larger the engine the more oil it needs to run better. Ive got an os wankel and i boost the oil content in the fuel i run in it to 25% it helps keep it cool and it runs better.