In general, all these elements must be assessed via a limited ‘window’ into the subsurface world, which is sometimes provided by one (or possibly more) exploration wells. These wells present only a one-dimensional segment through the Earth and inferring three-dimensional characteristics from them is one of the most fundamental skills in petroleum geology. Explorationists employ multiple geophysical methods, as each can provide unique information regarding the earth’s subsurface and the potential hydrocarbon prospects contained therein. These methods can be employed at various stages of the exploration cycle, and each can have widely different costs and timeframe to employ, depending on the location and difficulty of access of the prospect area. Each method provides unique information regarding density, resistivity, and other earth properties.