Bottomhole pressure refers to the pressure at the bottom of a borehole. it is caused by the hydrostatic pressure of the wellbore fluids and, sometimes, by any back-pressure held at the surface, as well the well is shut-in with blowout preventers. When drilling mud is being circulated, bottomhole pressure is the hydrostatic pressure plus the remaining circulating pressure required to move the mud up the annulus. The pressure can be recorded by a bottomhole pressure gauge.