PURPOSE: To provide a lubricating oil having excellent compatibility which comprises a synthetic hydrocarbon lubricating oil, a load-resistant additive, and a particular liquid modified ethylene/α-olefin random copolymer.

CONSTITUTION: 100pts.wt. liq. ethylene/3W20C α-olefin random copolymer having an ethylene content of 30W75mol.%, an intrinsic viscosity of 0.01W0.3dl/g, a number-average MW of 300W5,000, and an MW distribution of 1.1W4 is graft- modified with 0.2W50pts.wt. 3W10C unsatd. carboxylic acid (derivative) (e.g., acrylic acid) to prepare a liq. modified ethylene/α-olefin random copolymer (C) having a number-average MW of 310W5,000, an intrinsic viscosity of 0.01W0.3dl/g, and an MW distribution of 1.2W3. 100pts.wt. synthetic hydrocarbon lubricating oil (A) (e.g., polydecene-1) is blended with 0.1W20pts.wt. load-resistant additive (e.g., dibutyl phosphate) and 0.8W200pts.wt. component C in a C to B weight ratio of 0.05W200.