By Grade do you mean the API gravity? Thinner versus thicker?
That is part of the qualities that vary the value.
I have no idea what api gravity means. I think I meant "thinner vs. thicker" ..... I see terms like "light/sweet crude" and "heavy" and "brent crude" in various oil related stories which I've always assumed to have something to do with the thickness of oil, which then has an impact on the ease or difficulty of refining that oil into other products.
This is one of those areas I have literally zero knowledge in which is why I'm asking what are likely very basic/rudimentary questions.