Carbon black morphology, surface activity and loading have been varied systematically to study the effects on an SBR formulation. The surface activity of five commercial grades of carbon black was varied by heat treating the standard grade samples at 1100°C and 1500°C in an inert atmosphere. Measurements on carbon black-elastomer interaction were based on a parameter I, defined elsewhere. The parameter I exhibited the previously reported correlation with known indicators of the surface activity of carbon blacks. The heats of adsorption by inverse gas chromatography at infinite dilution have been found useful as a measure of the carbon-black surface energy related to rubber interaction. These measurements have been employed in conjunction with carbon-black morphology and loading to develop a surface-area-modified and a surface energy-modified effective volume fraction V′ and ψ, respectively. The parameter V′ was utilized to explain the variation of the dynamic elastic modulus E′ at 1 % double strain amplitude (DSA) for all rubber compounds. The parameter ψ was used to explain the variation of E′ at 25% DSA and the factor σ in the calculation of I. The parameters V′ and ψ provide a model for the estimation of I from fundamental carbon-black morphological properties and surface energy.