The first year all cars at Indy ran with petroleum oil. No more castor bean oil.
The Mobil oil for Indy was selected from random Mobil gas stations and certified as such by the AAA that also ran the Indy 500 and most other racing in the US in those years.
Safety was not a consideration, haha. As much as I'd love to, I don't think I could ever consider taking one of those things out on track. Although, in the moment, I'd probably be stupid enough to do it.