What kind of oil do you put in lawn mowers - 2 stroke or 4 stroke?

Almost all lawn mowers are 4 stroke engines that use regular gasoline (no additives except maybe some StaBil when you store it for winter) and ordinary motor oil, the same used in cars in the crankcase. Usually you would put 10W30 or 10W40 in their crankcases. Briggs and Stratton engines are on most lawn mowers, though Tecumseh is also common. Some have Honda small engines. I suppose two stroke lawn mowers exist but they are the vast minority. You do not add 2-stroke oil to the gas like a chain saw or weed eater. If the mower does happen to be a 2-stroke, I'm certain it would be plainly labeled, probably on the gas cap.