regular 30 W, it says elsewhere on the Net, at least for some models in your category
SAE-30
Briggs and stratton engines use different oils depending on the temperature to which the engines will be used. Generally sae30 oil should be used for mower engines
Generally Briggs calls for 30W but you can also use 10w30 especially if you are using it in cool temperatures.
You should always have 20 fluid ounces of oil in a Briggs and Stratton 5.5 HP lawn mower. This equals out to roughly 1.6 quarts.
The way to drain gasoline from a Briggs and Stratton lawn mower is to take the oil cap off and drain the oil. From there, run a rubber hose into the drain and siphon the rest of the oil and gas out.
If its a new mower take it back to where you bought for warranty If you mess with it you will forfeit your warranty.
10w - 30
There are two bolts holding it on to the block. You may have to remove some shrouds to get to it.
I have a push mower with a 4.5 horse on it and it uses a champion j19lm.
take the old plug to a mower parts store & tell them you need a matching one for a push mower
it takes 20w50 motor oil
If it's compatible just take one off and put the other in it's place.