Seafoam is multi purpose. If you are planning on doing an Oil change wiht in a hundred miles yes you can add it to the oil, it is like an engine flush, and yes you can add it to the gas, its liek any other fuel system cleaner. On my 95 Tbird i would put half of the seafoam in the break booster line, and the rest in the tank, and every 4 months put a whole bottle in the gas tank, not much smoke came from the exhaust after a while from doing the seafoam every year,