is a system of four standard classifications for rubber oils, based on content of saturated hydrocarbons, polar compounds, and asphaltenes, as described by ASTM-D-2226. The classifications are as follows:

Hydrocarbon Type, mass %
ASTM Type Oil	Saturates	Polar Compounds	Asphaltenes
101 (highly aromatic)	20.0 max.	25 max.	0.75 max.
102 (aromatic)	20.1-35.0	12 max.	0.50 max.
103 (naphthenic)	35.1-65.0	6 max.	0.30 max.
104 (naphthenic or paraffinic)	65.1 min.	1 max.	0.10 max.

Type 104 oils are subclassified into types 104A and 104B for styrene-butadiene rubber (SBR) only. Type 104A oils have a viscosity-gravity constant (VGC) greater than 0.820 (ASTM-D-2501), and are naphthenic; Type 104B oils have a VGC of 0.820 max., and are paraffinic

Also see aromatic.