Use straight 30 weight non-detergent. Not 10W-30.
What Type Of Oil Do I Put In A Push Mower?
How do I change the oil in a "Weed Eater Push Mower, 500 Series Briggs & Stratton 5.0 Gross Torque 158"
Consult your user's manual. If you don't have one, you might try checking the Internet URL of the manufacturer of the engine on your push-mower. Most can be expected to use SAE 30 weight oil in a four-cycle engine, and a specific quantity of any reasonable brand of two-cycle oil mixed with the specific quantity of gasoline specified in your owner's manual, and sometimes found on the gasoline tank of the lawn mower.