Styrene alkylmethacrylate succinimide phosphoric acid additives are synthesised and evaluated for use in multigrade crankcase lubricating oils as multifunctional viscosity index improvers having both antioxidant and dispersant properties. The synthesis is based on reacting styrene alkylmethacrylate (prepared by the reaction of styrene and 2-ethylhexylmethacrylate at different styrene/methacrylate mole ratios under various reaction conditions) with maleic anhydride and tetraethylenepentamine in the presence of phosphoric acid. Comparative evaluation of the properties of the synthesised products (e.g., viscosity properties, shear stability, oxidation stability and dispersive power) with commercial additives showed they were suitable for use as viscosity index improvers.