We have investigated the oxygen and hydrogen chemisorption properties and catalytic activities of the (12, 9, 8), (10, 8, 7), (654) and (321) platinum crystal surfaces which have (111) terraces, (410), (310) and (210) step orientations with 4.5, 5.9, 9.1 and 20% kink concentrations respectively. A UHV apparatus equipped for TDS, AES and LEED was utilized in these studies as a low pressure (10 −5–10 −6 Torr) flow reactor. Partial oxidation of the terraces at 800°C in 10 −7–10 −6 Torr of O 2 enhanced the initial rates of cyclohexene hydrogenation and dehydrogenation and cyclohexane dehydrogenation. The ordered, (√3 × √3)-R30°-O, oxygen layer was partially subsurface, strongly bound ( E d ~ 60 kcal mole −1 in zero coverage limit) and completely stable under reaction conditions in excess H 2. The enhancement in dehydrogenation activity at 150°C was greatest on the (10, 8, 7) platinum crystal surface with (310) step orientation (5.9% kinks). With a constant 5-atom terrace width the maximum activity shifted to higher oxygen coverage with increasing kink concentration. Strong chemisorption of hydrogen at kink sites was correlated with the greater resistance to self-poisoning of kinked surfaces as compared to Pt(111) and stepped Pt(557).