A gear pump uses the meshing of gears to pump fluid by displacement.They are one of the most common types of pumps for hydraulic fluid power applications.

Gear pumps are also widely used in chemical installations to pump high viscosity fluids. There are two main variations; external gear pumps which use two external spur gears, and internal gear pumps which use an external and an internal spur gears (internal spur gear teeth face inwards, see below).