A superactive acidic bimetallic catalytic composite, comprising a combination of catalytically effective amounts of a platinum group component, a tin component and a computed amount of a halogen component with a porous carrier material, is disclosed. The platinum group and tin component are present in the composite in amounts, calculated on an elemental basis, of about 0.01 to about 2 wt. % platinum group metal and about 0.01 to about 5 wt. % tin. The amount of the halogen component is selected as a function of the surface area of the porous carrier material and of the moles of tin contained in the composite in accordance with a hereinafter disclosed relationship. Moreover, the tin component is uniformly dispersed throughout the porous carrier material in a particle size having a maximum dimension less than 100.degree. A, substantially all of the platinum group component is present as the elemental metal and substantially all of the tin component is present in an oxidation state above that of the elemental metal. The principal utility of this superactive acidic bimetallic composite is in the conversion of hydrocarbons, particularly in the reforming of a gasoline fraction to produce a high octane and aromatic rich reformate. A specific example of the superactive acidic bimetallic catalyst disclosed is a combination of a platinum group metal, tin and chlorine with an alumina carrier material, wherein the tin component is uniformly dispersed throughout the alumina carrier material in a positive oxidation state and in a relatively small particle size and wherein the composite contains, on an elemental basis, about 0.01 to 2 wt. % platinum metal, about 0.01 to 5 wt. % tin and chlorine in an amount determined as a function of the surface area of the alumina and of the mole content of tin in accordance with an equation herein specified.