It depends on the area you live in. You need to find out how to change the oil in advance. SAE 30- is the most common for small engines of warmer temperatures. SAE 10W-30 is for a versatile range of temperature, normally taken for the cold weather. SAE5W-30 is for multiple temperatures. SAE 5W-30 is for cold temperatures. Vanguard 15W-50 is for continuous use and varying temperatures outside. Modern mowers don’t use too much oil and cut emissions.