Crude oil and natural gas are hydrocarbons that originate from algae, plankton, and other organic material. This biologic material settles to the bottom of a sea, is incorporated into the mud, and is subsequently buried by thick layers of sediment. The weight of the overlying sediment increases the temperature and pressure of the organic-rich mud. If these temperatures and pressures are sustained for long periods of time (~10 million years), the organic material is converted into kerogen and bitumen. As temperatures continue to increase, the kerogen undergoes a process called catagenesis (also called “thermal cracking”) in which it is converted into crude oil. Ideal temperatures for crude oil formation are called the “oil window,” and are approximately between 150° and 300°F (65° and 150°C). Natural gas begins to form at temperatures higher than approximately 300°F (150°C). Click to enlarge image at right.