Water finds cracks in the sea floor that it move down in; as it get deeper down in the earth, it gets hotter. Once water gets hot enough, it vaporizes, turns to gas form, and becomes less dense then the medium it is surrounded by, and starts coming back up to the surface of the earth. Once it rises, it cools down, and goes back to liquid form. Some of that water finds itself in pockets under ground, under heavy pressure, where it turn into oil. Even though we drill out that oil, these reservoir will refill itself over time, as more water vapor is pushing it self into the now empty reservoir.
Water finds cracks in the sea floor that it move down in; as it get deeper down in the earth, it gets hotter. Once water gets hot enough, it vaporizes, turns to gas form, and becomes less dense then the medium it is surrounded by, and starts coming back up to the surface of the earth. Once it rises, it cools down, and goes back to liquid form. Some of that water finds itself in pockets under ground, under heavy pressure, where it turn into oil. Even though we drill out that oil, these reservoir will refill itself over time, as more water vapor is pushing it self into the now empty reservoir.
Under the right conditions. Inject water, sand and chemicals under high pressure, and as a result oil is created.
If it is contaminated under pressure, it will be forced upward if there is a opening that way, until the pressure has been released.