I guess you can get that Great Merchant who gives 3 oil per turn is it? I haven't been able to find a CS with Oil when I need it or don't have it. At times if I play too slow and peaceful I can't get Oil Units for War which bothers me. It seems that the best way is to have early wars and claim more land to get oil. Thanks for telling me about the 1 unit per Trade though as I didn't know the AI would sell it to me like that. Tedious but better than not having Oil.