The oil that is commercially drilled throughout the world forms from tiny organisms that died long ago and have been forced deep into the earth over a period of millions of years. Oil is contained within deposits of rock which have a porous nature that has allowed them to "soak up" oil into the extra spaces within them. Oil is forced into the spaces in this porous rock over time by the natural movements of the earth, and enclosed within the area by surrounding non-porous rock through which it cannot permeate. In determining prospective places in which to drill for oil, companies such as Western Pipeline Corp must first determine as accurately as possible where such reservoirs of oil are located. Natural oil's position deep within the earth makes the process of locating it challenging, and numerous techniques have been developed to help determine where to drill.

Geologists are always seeking out new ways to determine which conditions are most indicative of oil reservoirs. Surface features and surface rocks have always been a component of oil geologists' analyses in determining the location of oil deposits. Older methods entailed analyzing the soil composition as well as rock and surface features, possibly in combination with small scale drilling. Today, the surface features remain an important part of locating oil reservoirs, though geologists also interpret data from satellite images.

A few methods are used to locate oil today, including the use of magnetometers, gravity meters and seismology. Magnetometers are instruments which measure the intensity of magnetic fields, and can provide important clues about the presence of oil. Minor changes in the Earth's magnetic field which possibly signify the presence of flowing oil can be detected using magnetometers. Similarly, gravity meters measure small changes in the gravitational field that may suggest the presence of moving oil.

The most common method used to locate an oil reservoir is seismic survey. Seismology is a science dealing with the analysis of vibrations deep within the earth and most notably involves the study of earthquakes. Seismology helps locate oil reservoirs both on land and under water using shock waves which reflect off of surfaces at varying speeds, with the speed indicating the density of the surface. Sensitive equipment is used to detect the reflection of these shock waves, and the data is then analyzed in effort to obtain a better understanding of the types of rock lying beneath the surface.

While methods of locating oil reservoirs have improved with time and technology, a fail proof method has yet to be discovered.