A hydraulic fluid reservoir (10, 10′, 10″, 10′″) comprises a body 12, 12′, 12″ 12′″) defining a variable volume chamber having one end portion movable with the level of fluid in the chamber. A biasing member (18, 18′, 18″, 18′″) acting on a traction rod (16, 16′, 16″, 16′″) extending from the movable end portion restrains movement thereof under fluid pressure. The fluid pressure in the variable volume chamber advantageously counterbalances the force of reaction in the biasing member (18, 18′, 18″, 18′″).