Abstract: A method for improving thermo-oxidative stability and elastomer compatibility in an apparatus lubricated with a lubricating oil by using as the lubricating oil a formulated oil including a lubricating oil base stock. The lubricating oil base stock includes a multi-aromatic base stock of the formula: R1—R2—(X—R2)n—R1 wherein each R1 is the same or different and is a terminal group, each R2 is the same or different and represents a substituted or unsubstituted aromatic moiety; each X is a linking moiety that is carbon-carbon single bond or a linking group, n is a number from 1 to 2000, and the ratio of the total number of aromatic ring carbon atoms to aliphatic carbon atoms in said formula is greater than 0.32:1. The multi-aromatic base stock has a kinematic viscosity greater than 20 mm2/s at 100° C.