Well logging is a means by which oil and gas companies gather detailed information about the layers of rock they drill through. The well logs can be created using a variety of tools for collecting seismic, electrical, electromagnetic, or radar signals sent from the borehole to a receiver. Well logging can also be based on visual inspection of sample brought up from the borehole. Specialists can then analyze this data to make the judgment with greater certainty of whether or not hydrocarbons are present in the well.