Compressor oils with high viscosity index

A method of increasing the energy efficiency of an air compressor, the method comprising:

• operating the air compressor with a compressor oil, wherein the compressor oil comprises:
• (i) 1 wt. % to 30 wt. % of a polyalkyl methacrylate-based viscosity index improver consisting of:
• (a) 0 wt. % to 25 wt. % of methyl methacrylate;
• (b) 75 wt. % to 100 wt. % of at least one straight-chained or branched C10-18 alkyl (meth)acrylate;
• and
• (c) 0 wt. % to 2 wt. % of at least one straight-chained or branched C5-9 alkyl (meth)acrylate or at least one straight-chained or branched C20-24 alkyl (meth)acrylate,
• wherein a weight average molecular weight (Mw) of the polyalkyl (meth)acrylate-based viscosity index improver is in a range of 5,000 g/mol to 400,000 g/mol;
• (ii) 70 wt. % to 99 wt. % of a base oil, wherein the base oil is an oil of American Petroleum Institute (API) group II, III, IV, or V, or a mixture thereof;
• and
• (iii) optionally, up to 2.5 wt. % of a performance package comprising one or more further additives,
• wherein the compressor oil has a viscosity index of at least 140.