If you've ever been in a hurry before mowing your grass, you may have inadvertently poured oil into the gas tank. Lawn mowers are four-stroke engines, meaning they burn pure gasoline instead of an oil and gasoline mixture like two-stroke engines. If oil gets in a lawn mower engine and you run the lawn mower, you may damage the engine. Removing oil from the gas tank isn't difficult. You can continue mowing your lawn within the hour.
Push the lawn mower to a well-ventilated area outside. Grasp the spark plug wire connector to pull it off the spark plug.
Empty the oil out of the lawn mower according to the oil change instructions. Typically you must turn the lawn mower on its side to drain the oil out of the reservoir into a container.
Drain the oil and gas mixture from the gas tank. Either tip the lawn mower on its side and drain the mixture into an approved container, or siphon the mixture into an approved container using a siphon hose.
Refill the oil reservoir to the appropriate level as determined by your lawn mower's operation manual. Refill the gas tank with new gas.
Push the spark plug wire connector back onto the spark plug.
Prime the lawn mower if applicable, and start the engine. You may notice white smoke coming out of the mower's exhaust for a split second as any minute quantities of oil are burned in the engine. This should quickly subside.