Hydrocarbyl substituted C.sub.4 to C.sub.10 monounsaturated dicarboxylic acid, anhydrides or esters, e.g. polyisobutenyl succinic anhydride, preferably made by reacting polymer of C.sub.2 to C.sub.10 monoolefin, preferably polyisobutylene, having a molecular weight of about 1500 to 5,000, preferably with a C.sub.4 to C.sub.10 monounsaturated acid, anhydride or ester, preferably maleic anhydride, such that there are 1.05 to 1.25 dicarboxylic acid producing moieties per molecule of said olefin polymer used in the reaction mixture. The resulting materials are useful per se as oil additives, or may be further reacted with amines, alcohols, amino alcohols, boric acid, etc. to form dispersants.