The new refrigerant fluids are generally not compatible with traditional mineral oils used for the lubrification of compressors. Different typologies of oils have been proposed, such as polyalkylene glycol (PAG), alkylbenzene (AB), and polyol ester (POE) oils. New thermodynamic models are necessary to describe well the behavior of these fluids, but at the moment only few experimental data are available in the literature. The work presented in this paper is part of our research program aimed to evaluate the solubility of refrigerants in commercial oils. The density of five different pentaerythritol esters is presented, which are used as components of the commercial POE oils (i.e., pentaerythritol ester of butyric acid (PEC4), pentaerythritol ester of valeric acid (PEC5), pentaerythritol ester of hexanoic acid (PEC6), pentaerythritol ester of heptanoic acid (PEC7), and pentaerythritol ester of octanoic acid (PEC8)). The experimental compressed liquid density data were correlated by means of a particular equation that is also presented in this paper.