The invention relates to liquid sulphur-containing antioxidants and to compositions comprising them. The novel lubricant compositions comprise the reaction product of a selected group of 5-tert-butyl-4-hydroxy-3-methyl(or tert-butyl)phenyl substituted carboxylic acid esters with thiodiethylene glycol and a mono-hydroxy alcohol with a carbon chain length higher than 4 C-atoms. The novel lubricant compositions are highly resistant to oxidative degradation and are capable of reducing the negative effects of deposits, such as black sludge, in motor combustion engines, particularly spark ignition internal combustion engines.