Again this oil is not for the space program guys. Take used oil from your car. Dump it in your mower. Will be just fine. Farmers have been doing this for decades.
Long ago I had one of the last Homelite 21" SP mowers with cast aluminum deck and about 4.5 HP B&S engine. 1988 I believe. Purchased from Monkey Wards just as the business was collapsing. The oil fill/check was a long tube and dipstick. With fresh oil and oil splashed up the tube (especially after adding oil) I found it impossible to read the oil level when oil in the tube wetted the dipstick. Overfilled, grossly. That was quite something when suddenly it ingested the excess oil. Buried 4 houses (over an acre) in blue smoke in seconds. Neighbors were reaching for 911. Always wondered if I could repeat that smoke screen? Never tried.
Drained oil to reasonable levels, engine recovered.
From then on I only put used Mobil-1 15W-50 from my VW Golf in that engine. Something that was dark enough I could read the dipstick.
About 10 years later the aluminum deck cracked. Must have been from my inferior oil.
A friend happily put my engine on another deck for his own use. Engine was still running great, not using oil.