The use as an anti-wear additive and/or friction modifier in a non-aqueous lubricant composition and/or in a fuel composition of at least one long chain fatty acid ester of a hydroxy carboxylic acid in which the long chain fatty acid has at least 4 carbon atoms and the ester is an oil-soluble ester of a mono- or poly-hydroxy carboxylic acid having 1 to 4 groups which are independently carboxylic acid groups or lower hydrocarbyl esters thereof and in which, when the hydroxy carboxylic acid is a mono-hydroxy carboxylic acid, the ester has a long chain fatty acid ester moiety of the hydroxy group of the hydroxy carboxylic acid and, when the hydroxy carboxylic acid is a poly-hydroxy carboxylic acid, the ester has independently long chain fatty acid ester moieties of one or two of the hydroxy groups of the poly-hydroxy carboxylic acid. Also, a non-aqueous lubricant composition and a fuel composition for an internal combustion engine which comprises at least one of said long chain fatty acid esters.

A liquid anti-friction composition includes an ester product having a number average molecular weight that is greater than 3800 g/mol, and obtained by subjecting a mixture that includes diglycerol, a monobasic acid component, and a dibasic acid component to an esterification reaction. The monobasic acid component includes at least one C.sub.14-C.sub.24 branched chain fatty acid.

A liquid anti-friction composition includes an ester product having a number average molecular weight that is greater than 3800 g/mol, and obtained by subjecting a mixture that includes diglycerol, a monobasic acid component, and a dibasic acid component to an esterification reaction. The monobasic acid component includes at least one C.sub.14-C.sub.24 branched chain fatty acid.