The stable form of adsorbed sulfur species and their coverage were investigated on Rh, Ni, and Rh-Ni binary metal surfaces using density functional theory calculations and the ab initio thermodynamics framework. S adsorption, SOx (x = 1-4) adsorption, and metal sulfide formation were examined on Rh(111) and Ni(111) pure metals. Both Rh and Ni metals showed a preference for S surface adsorption rather than SOx adsorption under steam reforming conditions. The transition temperature from a clean surface (<1/9 ML) to S adsorption was identified on Rh(111), Ni(111), Rh1Ni2(111), and Rh2Ni1(111) metals at various P(H-2)/P(H2S) ratios. Bimetallic Rh-Ni metals transition to a clean surface at lower temperatures than does the pure Rh metal. Whereas Rh is covered with 1/3 ML of sulfur under the reforming conditions of 4-100 ppm S and 800 degrees C, Rh1Ni2 is covered with 1/9 ML of sulfur at the lower end of this range (4-33 ppm S). The possibility of sulfate formation on Rh catalysts was examined by considering higher oxygen pressures, a Rh(221) stepped surface, and the interface between a Rh-4 cluster and CeO2(111) surface. SOx surface species are stable only at high oxygen pressure or low temperatures outside those relevant to the steam reforming of hydrocarbons.