Lactone modified adducts are made by first reacting a non-polymerizable lactone or thiolactone and then a polymerizable C.sub.5 -C.sub.9 lactone with an aminated hydrocarbyl substituted C.sub.4 -C.sub.10 monounsaturated dicarboxylic acid producing material, e.g. a polyisobutenyl succinimide, which, in turn, preferably is made by reacting a polymer of a C.sub.2 to C.sub.10 monoolefin, preferably polyisobutylene, having a molecular weight of about 700 to 5,000 with a C.sub.4 to C.sub.10 monounsaturated acid, anhydride or ester, preferably maleic anhydride, such that there are about 0.7 to 2.0 dicarboxylic acid producing moieties per molecule of said olefin polymer used in the reaction mixture, and then reacting the substituted acid, anhydride or ester with an amine. The resulting adducts are useful per se as oil soluble dispersant additives. They are also useful in fuel and lubricating oil compositions, as well as in concentrates and additive packages.