Abstract 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) and isobutane (R600a) regarded as green refrigerants have received much attention in the refrigeration industry. Phase equilibrium between refrigerant and lubricant has a critical impact on the performance of a compression-refrigeration cycle. To determine the influence of the lubricant structure, pressure and temperature on phase behavior of refrigerant/lubricant mixtures, a long-term systematic research program on the phase equilibrium of refrigerant/lubricant mixtures has been carried out in our laboratory. In this work, solubilities of R1234yf and R600a in pentaerythritol tetranonanoate (PEC9) were measured from 293.15 to 348.15 K using isochoric saturated method. The results show that there was no color change, no sediment generation and no stratification in the whole experiment. Solubilities rise with an increase in pressure and a decrease in temperature. Solubilities of R600a are higher than those of R1234yf. The experimental data were correlated by the nonrandom two-liquid (NRTL) model. Comparing solubilities of the same refrigerant in different linear-chained pentaerythritol esters, solubilities increase with rising length of the linear chain of the carboxylic acid for pentaerythritol esters.