Low carbon steel (C14) gears in the untreated condition as well as those heat treated by different methods (carburized, Sursulf treated, Tufftride treated and duplex treated in two different ways) were tested in a back-to-back gear test rig. The duplex treatments investigated are carburizing followed by a Sursulf treatment, and carburizing followed by a Tufftride treatment. The purpose of carrying out two treatments at a time on the gear specimens is to see whether the advantages of both treatments can be obtained. For the treatments under investigation the contact stress-pitting life curves have been established and wear curves have been generated. At any stress level, the duplex treated gears exhibited the longest life as determined by the formation of the first pit. No significant difference between the behaviours of the Sursulf and Tufftride treated gear specimens was observed with respect to surface endurance. A similar trend was observed with respect to carburized and the two duplex treated gear specimens. The wear characteristics of C14 steel gears can be substantially improved by the duplex method of carburizing and Sursulf treatment. © 1991.