An improved dispersant material for mitigating crude oil fouling comprises a reaction product of a polyamine and a polyisobutylene succinyl anhydride made with a polyisobutylene having a vinylidene double bond content of at least 50%. The reaction product has an active nitrogen atom content of at least about 2% by weight. The reaction product is prepared by thermally reacting the polyisobutylene with maleic anhydride to produce said polyisobutylene succinyl anhydride and thereafter reacting the polyisobutylene succinyl anhydride with a polyamine having 5 to 7 active nitrogen atoms.