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The dissociative adsorption of oxygen on the stepped Pt(533) surface has been investigated using supersonic molecular beams by measuring the initial dissociative sticking probability S[sub 0] as a function of incident kinetic energy E[sub i], angle Φ, surface temperature T[sub S], and S as a function of coverage Θ. By comparison with dynamical data available on the Pt(111) surface we have been able to establish that step sites dominate the dissociative adsorption process. S[sub 0](E[sub i]) for oxygen on Pt(533) at T[sub S]=200 in the energy range 52 meV-1.4 eV shows a similar functional dependence to results on Pt(111), however, the magnitude of S[sub 0] on Pt(533) is significantly greater at all energies. The measurement of S[sub 0](Φ), scattering in a plane perpendicular to the step direction at E[sub i]=1.18 eV at T[sub S]=350 K, reveals a strong and asymmetric angular dependence which contains contributions associated with activated adsorption and dissociation of the chemisorbed precursor on the (111) terraces, and a second contribution associated with activated dissociation through a similar channel at the step sites. The latter exhibits a maximum in S[sub 0](Φ) at 35°, near the angle corresponding to the normal of the (100) step plane. S[sub 0](T[sub S]) at E[sub i]=1.18 eV and Φ=0° reveals a much smaller temperature dependence in the range 150>T[sub S](K)>800 on Pt(533) than on Pt(111). At E[sub i]=1.18 eV and Φ=0° ca. 15%-25% of dissociation takes place through molecules impinging directly at step sites. The remaining fraction dissociate through activated adsorption of the chemisorbed species on the (111) terrace and subsequent partition between desorption, and dissociation at step sites. Dissociation of the chemisorbed precursor on the (111) terrace appears highly activated, a result which is consistent with theory. The rapid decrease in S[sub 0](E[sub i]) observed below 0.15 eV on Pt(533), observed also on P... [ABSTRACT FROM AUTHOR]