When I bought my first automobile, a used 1957 Chevrolet Bel Air (boy do I wish I still owned it!), there was no owners manual. I didnt worry about what oil to use since I was just starting my career in the oil industry and I planned to use my companys brand(Richfield Oil). Since then, Ive owned 15 other automobiles, pickup trucks, SUVs and vans. In each case, Ive either used the brand of the company I worked for (Unocal and Pennzoil) or oil formulations from customers of my additive company (Edwin Cooper/Afton and Chevron Oronite).