  We predict the volume of liquid recovered from different-shaped prismatic
channels following gas displacement. This recovery factor depends strongly on
the contact angle at which the gas-liquid interfaces meet the walls of the
channel. We show that scaling the contact angle by a critical value, dependent
on the channel shape, leads to a master curve for the recovery factor.} Our
numerical simulations with the Surface Evolver are supported by theoretical
calculations for the capillary entry pressure in a channel with a triangular or
rectangular cross-section and for the interface shape in a "scalloped"
triangular channel formed between three parallel cylinders.
