Geophysicists play an important role in the oil and gas industry as they help find underground oil and gas deposits by creating a clear picture of what is below the earth’s surface. Using physical methods (seismic, gravitational, magnetic, electric) they measure the physical properties of subsurface earth to detect or infer the presence of oil or gas. The most common way to create a clear picture of the earth's subsurface is through the seismic method whereby shock waves that are set off at the surface resonate through the earth, and the returning echo can be used to tell what is beneath the surface. Geophysicists are usually classified into three categories: acquisition, processing and interpretation. A strong geoscience, physics, or mathematics background is necessary for a career in geophysics.