The New Texas Oilfield is a region that is made up of two towns, Verdammter Platz and Diep Gat. It is protected by Desert Patrol. It is one of the only places to get crude oil, and usually your first chance to buy cars.
Please note that these cities have by default an unreliable source of market-ready fuel, creating a very real possibility of battling through difficult territory just to reach the best shops to buy cars, only to find you cannot take them far enough to reach another fuel source. The city of Hara to the north has a thriving fuel production industry, and can be beneficial to visit beforehand to avoid this massive (potentially game-ending) financial dead end circumstance.