Oil is extracted by five main machines : a fixed platform, a semi-submersible, a spar, a TLP (Tension Leg Platform) and a FPSO (Floating Production Storage and Offloading unit). The oil is normally below the suface of the crust in a thing called a oil baisin, which takes tens of millions of years to fill up, since oil is a non-renewable soure of energy and current known oil resouces are said to run out in around just 50 years.