Suggested is a method for enhancing energy efficiency of engines by applying to said engines a lubricant composition containing (A) carboxylic esters derived from the reaction of mono-, di- and/or poly alcohols with mono- and/or dicarboxylic acids, together with an additive blend (B) comprising at least two different additives (a) and (b) together, whereby compound (a) is selected from dithiophosphates, and compound (b) is selected from alkylated phosphorothionates, on condition that the total amount of the additive blend (B) is below 0.1 wt %, calculated on the weight of the whole composition.