The reactions of ethanethiol (C/sub 2/H/sub 5/SH) on Mo(110) under ultrahigh vacuum have been investigated by temperature-programmed reaction, X-ray photoelectron, and high-resolution electron energy loss spectroscopies. Electron energy loss spectroscopy indicates that the S-H bond in ethanethiol dissociates below 120 K to form a surface ethyl thiolate (C/sub 2/H/sub 5/S). At low coverages the ethyl thiolate decomposes to atomic carbon, atomic sulfur, and gaseous H/sub 2/, with decomposition complete below 350 K. At high coverages, the surface thiolate decomposes during temperature-programmed reaction via three competing pathways: hydrogenolysis at 300 K to gaseous ethane, dehydrogenation at 340 K to gaseous ethylene, and decomposition to surface carbon, surface sulfur, and gaseous dihydrogen. Notably, the presence of surface atomic sulfur is not necessary for selective formation on clean Mo(110); the thiolate remains intact up to the temperature of hydrogenolysis onset. The last pathway proceeds via a hydrocarbon fragment(s) which decomposes at 570 K to gaseous H/sub 2/ and atomic carbon. At saturation, /approximately/ 75% of all irreversibly chemisorbed ethanethiol forms gaseous hydrocarbons. The coverage-dependent kinetics for ethanethiol decomposition are discussed in terms of electronic and site-blocking effects.