Why was there oil under Texas and was there more? Wildcatters would come to Texas and drill hole after hole. Some became rich, but some lost everything. The area that we now call Texas, has accumulated oil many times since the Paleozoic. Invading seas created coral reefs. These broad shallow shelves created conditions ideal for oil accumulation from the Paleozoic to Cenozoic.

So, even though drillers were finding oil, the oil was not from the same sources. For example, the oil in East Texas was caused mainly by Mesozoic (green colors on the map) to Cenozoic (yellow to orange) sediments. In West Texas, the oil is mainly from late Paleozoic reef and limestone structures. The geology of the state is important to reconstruct where the oil was formed and where the oil is today.