A compact fluid accumulator both stores a relatively large amount of fluid and provides good fluid pressure stability. The accumulator includes a piston slidably disposed in a cylinder having a fluid inlet/outlet at one end which communicates with a first chamber and one face of the piston. Engaging the opposite face of the piston, and disposed in a second chamber, is a compression spring. The second chamber is filled with a gas which is at atmospheric pressure when the accumulator is relaxed. When pressurized hydraulic fluid fills the first chamber, the piston moves against the pressure of the spring and gas in the second chamber. The present invention thus provides an accumulator having the relatively small size of a gas filled accumulator without the leakage problem of a super-atmospheric gas charge—the extra force being provided by the compression spring.