1. n. [Drilling]

Gas that rises to the surface, usually detected because it reduces the density of the drilling mud. Gas detectors, which the mud logger monitors, measure combustible gases (methane, ethane, butane and others). The mud logger reports total gas, individual gas components, or both, on the mud log. In extreme cases, gas visibly bubbles out of the mud as it returns to the surface. Because the mud does not circulate to the surface for a considerable time, sometimes lagging several hours after a formation is drilled, a gas show may be representative of what happened in the wellbore hours (or many feet) prior to the current total depth of the well.

See: drilling fluid,  total depth