I can't say because you don't mention the make & model of your mower.
I have a powered mower that takes regular petrol (gas) and it has an unscrew Oil Filler cap - this is a reliable indicator of not needing to mix oil with the fuel. I put Lawnmower engine oil in. The cap has the word OIL on the top. Petrol (gasoline) on its own goes in the fuel tank.
I have a baby tiller with no place to put engine oil - there's a big notice on the engine saying 50:1 which is the fuel:oil mixture. I mix the petrol (gas) with two-stroke oil in that ratio and pour it in the small fuel tank.
Peccavi, March 2009
