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 pt(delta+) 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.