Abstract: Lubricant compositions comprising certain mixtures of esters of pentaerythritol, di-pentaerythritol, tri-pentaerythritol and higher pentaerythritol oligomers are ideally suited for use with CO2 as refrigerant in heat transfer devices provided that at least 30% by weight of the esters are esters of pentaerythritol oligomers containing 4 or more pentaerythritol monomer units and wherein a majority of the alkylcarboxylate groups are straight chain C3-6 alkanoyl groups, such as n-pentanoyl. Said mixture of alkylcarboxylate esters are shown to not only have higher than expected viscosity and exceptional CO2 miscibility, but also possess excellent lubricity, film building properties and load bearing properties even as part of a lubricant/CO2 solution.