PURPOSE: To obtain a polymer composition of improved compatibility in oil by compounding specific types of an olefin-based polymer, a polar polymer, an aromatic material and a medium.

CONSTITUTION: This polymer composition comprises one or more oil-soluble olefin-based polymers (e.g. polyisobutene) exhibiting incompatibility evidenced by phase separation when combined with a non-polar oleophilic medium, one or more oil-soluble polar polymers (e.g. a polymer obtained by esterifying a maleic anhydride/styrene alternate copolymer with a long-chain primary alcohol and then reacting the obtained ester with 4-(3-aminopropyl)morpholine having N functionality, one or more substituted hydroxyaromatic materials (e.g. a polyisobutylene-substituted phenol) having one or more hydrocarbyl groups, and a non-polar oleophilic medium (e.g. a mineral oil).