Hydrocarbons are converted by contacting them at hydrocarbon conversion conditions with a trimetallic acidic catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a Group IVA component, a bismuth component and a halogen component with a porous carrier material. The platinum group component, Group IVA metallic component, a halogen component are present in the trimetallic catalyst in amounts respectively, calculated on an elemental basis, corresponding to about 0.01 to about 2 wt. % platinum group metal, about 0.01 to about 5 wt. % Group IVA metal and about 0.1 to about 3.5 wt. % halogen. The bismuth component is present in amounts corresponding to an atomic ratio of bismuth to platinum group metal of about 0.1:1 to about 1:1. Moreover, these metallic components are uniformly dispersed throughout the porous carrier material in carefully controlled oxidation states such that substantially all of the platinum group metal and bismuth components are present therein in the corresponding elemental metallic states while substantially all of the Group IVA metallic component is present therein in an oxidation state above that of the corresponding metal. A specific example of the type of hydrocarbon conversion process disclosed is a process for the catalytic reforming of a low-octane gasoline fraction wherein the gasoline fraction and hydrogen stream are contacted with the novel trimetallic catalyst disclosed herein at reforming conditions.