Novel dispersant mixtures are provided, having improved lubricating oil performance characteristics, comprising nitrogen or ester containing dispersants selected from the group consisting of oil soluble salts, amides, imides, oxazoline and esters or mixtures thereof, wherein a first dispersant comprises a long chain hydrocarbon substituted mono- and dicarboxylic acid or their anhydrides derived from polymers of C.sub.2 to C.sub.10 monoolefins wherein the polymer has a number average molecular weight of at least about 1300 and wherein the second dispersant component is derived from such polymers having a number average molecular weight of from about 700 to 1150. The relatively high molecular weight dispersant is provided with from about 1.05 to 1.25 moles per mole of polyolefin of an alpha or beta unsaturated C.sub.4 to C.sub.10 dicarboxylic acid or anhydride or ester thereof. The relatively lower molecular weight dispersant is provided with from about 1.2 to 2.0 moles per mole of polyolefin of an alpha or beta unsaturated C.sub.4 to C.sub.10 dicarboxylic acid, anhydride or ester thereof. It has been found that mixtures of such high molecular weight-low functionality dispersants and low molecular weight-high functionality dispersants provides a dispersant, suitable for use in oleaginous materials such as lubricating oils, which provide surprisingly improved engine performance properties.