Petroleum geology is the study of the origin, natural occurrence, movement, gathering of and exploration of hydrocarbon fuels, especially oil or petroleum. The main focus of petroleum geology is studying and finding oil.
Petroleum geology involves sedimentology, the study of how sand, mud and clay are deposited. The majority of rocks found on the Earth's surface are sedimentary rocks. Studying sedimentology helps petroleum geologists understand how the petroleum deposits found in sedimentary rocks came to be.
Another aspect of petroleum geology is stratigraphy, the study of the relationship between rock layers and the way they can move or shift. The movement of rock layers can affect where petroleum deposits are found, as well as the removal of the petroleum.