The aromatic content of oils has a moderate swelling effect
on rubber. ASTM Oil No.1 (Flash point 243°c, Aniline
point 124°c) has a swelling effect. ASTM Oil No.3
(Flash point 163°c, Aniline point 70°c) has a
severe swelling effect. Both oils are petroleum based
and are fully described in ASTM D471.