Hydrocarbons are converted by contacting them at hydrocarbon conversion conditions with an acidic multimetallic catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a tin component, a cobalt component, and a halogen component with a porous carrier material. The platinum group, tin, cobalt and halogen components are present in the multimetallic 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. % tin, about 0.1 to about 5 wt. % cobalt, and about 0.1 to about 3.5 wt. % halogen. Horeover, the catalytically active sites induced by these metallic components are uniformly dispersed throughout the porous carrier material and these components are present in the catalyst in carefully controlled oxidation states such that substantially all of the platinum group component is in the elemental metallic state, substantially all of the catalytically available cobalt component is in the elemental metallic state or in a state which is reducible to the elemental metallic state under hydrocarbon conversion conditions or in a mixture of these states, while substantially all of the tin component is present therein in an oxidation state above that of the elemental 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 a hydrogen stream are contacted with the acidic multimetallic catalyst disclosed herein at reforming conditions.