AbstractUsed oils constitute a potential health hazard. Every year several million tons of used oils are released into the environment. At present, environmentally friendly synthetic oils, e.g., esters, are used as alternatives to conventional oils produced from petroleum. The aim of the present work has been to synthesise ester oils and determine their properties, particularly in terms of their biodegradability. Using dimethyl adipate, dimethyl sebacate, and neopentyl glycol as starting materials, oligomer esters with different ranges of molecular mass were synthesised. The syntheses were based on transesterification reactions catalysed by calcium methoxide. The degree of oligomerisation was closely correlated with the molar ratio of the esterification substrates. The esters showed physicochemical properties appropriate for use as synthetic lubricants. Both adipic acid esters and sebacic acid esters are characterised by high biodegradability. The biodegradability depends only slightly on the degree of oligomerisation of the ester molecules. The esters studied were considered as environmentally friendly high‐performance functional fluids.