Isomerization of naphthenes

A process for isomerizing an isomerizable naphthalene hydrocarbon selected from the group consisting of C.sub.5 to C.sub.9 naphthenes which comprises contacting said hydrocarbon at isomerization conditions with a catalyst comprising a porous carrier material containing, on an elemental basis, 0.01 to 2 wt. % platinum group metal, 0.1 to 5 wt. % cobalt, 0.01 to 5 wt. % tin and 0.1 to 10 wt. % halogen, wherein substantially all of the platinum group metal, cobalt and tin are uniformly dispersed throughout the porous carrier material, wherein substantially all of the platinum group metal and cobalt are present in the elemental metallic state and wherein substantially all of the tin is present in an oxidation state above that of the elemental metal.