There's no guarantee there's oil in either place. Remember, oil is the product of organic matter being compressed under heavy pressure for millions of years. Even if microbes or their remains are discovered on Mars or Venus, which they haven't (definitively), there's no guarantee that there was life of any considerable biomass.

So I really wouldn't get my hopes up for extraterrestrial oil at all, sad as that may be. On the other hand, minerals and metals most certainly exist outside of Earth, so...?