Poly(C.sub.5 -C.sub.9 lactone) adducts are made by reacting a C.sub.5 -C.sub.9 lactone with a post reacted hydrocarbyl substituted C.sub.4 -C.sub.10 monounsaturated dicarboxylic acid producing material, e.g., a polyisobutenyl succinic anhydride, which, in turn, preferably was made by reacting a polymer of a C.sub.2 to C.sub.10 monoolefin, preferably polyisobutylene, having a number average 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 0.7 to 2.0 dicarboxylic acid producing moieties per molecular of said olefin polymer used in the reaction mixture, and then, post reacting the substituted acid, anhydride or ester with a polyol such as pentaerythritol or THAM. The resulting adducts are useful per se as oil soluble dispersant additives useful in fuel and lubricating compositions including concentrates containing the additives.