The reservoir drive mechanism in which oil is produced by the expansion of the underlying water and rock, which forces the oil into the wellbore. In general, there are two types of water drive: bottom-water drive, in which the oil is totally underlain by water; and edgewater drive, in which only a portion of the oil is in contact with the water. (2) An oil or gas reservoir in which pressure is maintained to a greater or lesser extent by an influx of water as the oil or gas is removed.