A correlation of the catalytic properties of three supported Pt catalysts with their physical properties, chemical composition, and adsorption properties is presented. The catalytic properties of 0.75 wt% Pt/silica, 0.89 wt% Pt/alumina, and 0.48 wt% Pt/molybdena are reported for the hydrogenolysis of cyclopropane and for the hydrogenations of ethene, 1,3-butadiene, and 2-butyne. The corresponding catalytic properties of the standard reference catalyst EUROPT-1, a 6.3 wt% Pt/silica, are reported for comparison. Pt/silica and EUROPT-1 each contained fully reduced Pt and were chloride free; their activities for structure-insensitive 1,3-butadiene and 2-butyne hydrogenations were in proportion to their respective Pt dispersions and product selectivities were identical. This intercatalyst comparison could not be extended to ethene hydrogenation because reaction over Pt/silica showed a kinetic discontinuity which is described in detail. Pt/alumina contained Ptδ+which had the effect of reducing activity in each hydrogenation reaction and of altering product selectivity in 1,3-butadiene hydrogenation. A condition was found under which this support effect was reversed. Cyclopropane hydrogenolysis over all four catalysts obeyed the Bond–Newham rate equation, and the rate coefficient varied with Pt particle size indicating the reaction to be structure sensitive. Pt/molybdena, the only catalyst having a wide range of Pt particle size, behaved in contrasting and predictable ways depending upon the structure-sensitive or-insensitive nature of the reaction under study.