A fuel pump is disclosed wherein a substantially cylindrical plunger bore is provided with an annular drain groove fluidically coupled to a drain duct. A pump plunger is driven by a drive system located in a separate mechanical compartment that holds a reservoir of lubricating oil. An annular seal is provided adjacent the drain groove substantially at the end of the bore and retained in position by a seal support. Exemplary embodiments provide the drain groove and seal as being positioned immediately adjacent one another so that the seal forms a lower wall of the drain groove.