The goal is to find a convergence of the geologic elements necessary to form an oil or gas field. Finding these subterranean features requires a careful blend of science and art. For example, structural geology involves gathering and interpreting information from above ground to deduce what lies underground. Subtle changes within the Earth's magnetic and gravitational fields also may signal the presence of petroleum traps. Seismic surveying involves sending sound waves underground and measuring how long it takes subsurface rocks to reflect them back to the surface.
Earth scientists use the data to create three-dimensional models of underground rocks.
Although sight and sound are the senses most frequently used in prospecting, smell also can come into play. A rank wildcat well, drilled in an unproven, frontier area, stands a one in 40 chance. Thus, although today's prospectors have better tools than their ancient counterparts, good luck still is a factor in the search for petroleum.