Abstract: A multi-chamber positive displacement pump comprises a unitary housing in which is formed a plurality of cylinders. A pumping plunger is slidably mounted in each cylinder to define a pumping chamber. Means are provided for reciprocating the pumping plungers in order cyclically to vary the volume of the pumping chambers to effect delivery of a pumped fluid from the pumping chambers. A delivery passage is connected to each of the pumping chambers to receive pumped fluid therefrom, the delivery passage comprising at least one gallery formed in the unitary housing and open to an end face of the housing and passageways which extend through the unitary housing from the galleries to the pumping chambers. The galleries are closed by an end plate which is secured to the unitary housing. Feed passages and working fluid passages may likewise be defined by combination of galleries in the end face and passageways in the unitary housing.