The stability of a hot forging lubricant determines its effectiveness during operation. Aqueous lubricants, which are increasingly popular because of environmental issues, contain an organic ingredient, a stabilizer, and other species including biocides and corrosion inhibitors. The stability of a model forging lubricant containing dipotassium o-phthalate and sodium silicate in water has been measured over a wide range of temperatures and initial concentrations. The oxidation of the organic species is correlated using kinetic analysis, which reveals that decomposition occurs through a first-order reaction with an activation energy of approximate to 58.2 kJ/mol. The kinetic result is consistent with a proposed free radical reaction mechanism that is also shown to be consistent with theoretical calculations and results reported for other types of lubricants.