Thickened water-glycol hydraulic fluids, which are generally suitable for use at system pressures of < 34.5 MPa have been used by the fluid power industry for over forty years. The principle reason for the use of this class of fluids is their outstanding fire safety properties. However, when higher system pressures are encountered and fire safety is required, a polyol ester or phosphate ester based fluid is usually selected. Recently, a proprietary, thickened water-glycol based fluid has been developed for use at system pressures of up to 34.5 MPa. The fire safety and performance testing results of this fluid will be described in this paper.