The compatibility of rubbers against reference oils - IRM 901 (Formerly ASTM No. 1 oil) IRM 902 & IRM 903 is a common test called for in material specifications.
The tests are often used to indicate compatibility against lubricating oils and greases, but are also a valuable quality tool to ensure consistency in rubber formulation.
Smithers Rapra has oils available in 5 litre or 25 litre containers