As the Gulf of Mexico began to develop millions of years ago, seawater entered the slowly sinking basin. At first, the very shallow seawater readily evaporated to produce salt deposits. As the basin continued to sink, the seawater became deeper and less likely to substantially evaporate and produce salt deposits. Sediments entered the sinking basin and buried the salt layers. The salt layers are less dense than most other sediments and rocks.
Many salt domes have a toadstool or umbrella shape, which allows for the accumulation of oil.
Formation of Salt Domes and Oil Traps. Many conditions are required for oil to form, accumulate and survive over geologic time. Not surprisingly, there are very limited resources of oil and natural gas. Most of the easy to find petroleum deposits have already been discovered. New discoveries are often in remote locations, usually offshore, and may require advanced technologies to recover.