Sum frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have identified at least two reaction pathways for benzene hydrogenation on the Pt(100) and Pt(111) single-crystal surfaces at Torr pressures. Kinetic studies at low temperatures (310-370 K) show that benzene hydrogenation does not proceed through cyclohexene. A Langmuir-Hinshelwood-type rate law for the low-temperature reaction pathway is identified. The rate-determining step for this pathway is the addition of the first hydrogen atom to adsorbed benzene for both single-crystal surfaces, which is verified by the spectroscopic observation of adsorbed benzene at low temperatures on both the Pt(100) and Pt(111) crystal faces. Low-temperature SFG studies reveal chemisorbed and physisorbed benzene on both surfaces. At higher temperatures (370-440 K), hydrogenation of benzene to pi-allyl c-C6H9 is observed only on the Pt(100) surface. Previous single-crystal studies have identified pi-allyl c-C6H9 as the rate- determining step for cyclohexene hydrogenation to cyclohexane.