The miscibility of POE68 and PVE68 oils with R-1234ze(E) has been investigated for the temperature and oil mass fraction ranging of –35~80 °C and 0~70 wt%, respectively. Mixture saturation vapor pressures are also measured and are shown to decrease with increase in mass fraction of the oil. The miscibility-test results indicate that the POE68 and PVE68 oils are completely miscible at mass fractions of the oil below 20% and 10%, respectively, for the entire temperature. Refrigerant-oil phase separations are observed for certain mass fraction of the oil and temperature ranges, indicating that the refrigerant-oils are not miscible.