Lubricating oil

A method of lubricating an article, comprising providing to the article a lube oil, wherein the lube oil comprises, as a base oil, an ionic liquid having an ion concentration of 1 mol/dm3 or more in an amount of 90 to 100 mass %, wherein the ionic liquid has a total acid value of 1 mgKOH/g or less and is represented by the formula Z+A− where Z+represents a cation and A− represents an anion;

• at least one of an antioxidant and an extreme pressure agent, wherein the cation (Z+) forming the ionic liquid is represented by any of the following formulae:
• wherein each of R1 to R6, which may be identical to or different from one another, represents a group selected from among a hydrogen atom, C1 to C18 alkyl groups which may each have an ether bond, and C1 to C18 alkoxy groups, wherein the anion (A−) forming the ionic liquid is BF4− or ((CnF2n+1−x)Hx)Y1Oz)2N−, wherein Y1 represents a carbon atom or a sulfur atom, wherein a plurality of Y1 are present, these may be identical or different from one another, a plurality of (CnF2n+1−x)Hx)Y1Oz groups may be identical or different from one another, n is an integer of from 1 to 6, x is an integer of from 0 to 13, and z is an integer of from 1 to 3 when Y1 is a carbon atom and 0 to 4 when Y1 is a sulfur atom, and
• wherein the article is an internal combustion engine, a torque converter, a fluid coupling, a radial bearing, a rolling bearing, an oil-retaining bearing, a fluid bearing, a compressor, a chain drive, a vacuum pump, a clock part, a hard disk apparatus, a refrigerator, a shock absorber, a corrosion prevention, a brake member, a sealing device, or an aerospace apparatus.