The combustion intensity of hydraulic fluids and mineral oil, methanol, ethanol, and heptane, ejected vertically up ward through a pressure-jet hollow cone nozzle and stabilized by a ring burner, has been characterized in terms of heat release rates. A relationship has been established between the chemical heat release rate, fluid exit velocity, and chemical heat of combustion. Mineral oil, along with some organic esters, has the highest combustion intensity as indicated by heat release rate, followed by esters (organic and phosphates), heptane, water-in-oil emulsion, ethanol, methanol, and polyglycol-in-water. Variations in combustion intensities in hydraulic fluids are found to be due to variations in the chemical structures and additives.