Abstract: A dual-piston fuel pump assembly includes a housing having an inlet to a primary chamber and an outlet from a pumping chamber. Between the primary and pumping chambers are interposed concentric inner and outer pistons. Each piston is independently spring biased toward the pumping chamber. The inner piston is mechanically driven by an engine associated reciprocating drive and pumping action occurs as a result of the spring operating on the inner piston. The position of the outer piston relative to the inner piston is determined by the pressure in the pumping chamber as regulated by the force of the spring operating against the outer piston. When pressure in the pumping chamber exceeds predefined limits, the outer piston opens regulator ports disposed on the inner piston to recirculate fuel back into the low pressure primary chamber. Additionally, the outer piston acts as an accumulator to dampen pressure spikes.