The thermodynamic behavior of mixtures R125/R290 and R134a/R290 having different composition in saturation state was considered. The existence of aseotropic mixtures containing 0,6 molar part of R125 and 0,4 molar part of R134a was mentioned. The dependences of saturated vapor and liquid temperatures` differences of mixtures on isobars from pressure and temperature are presented in pressure interval from 0,1 up to 3,5 MPa and temperature interval from 220 to 350 °C. The energetic efficiency of refrigerating plants` cycles using mentioned mixtures as working media was estimated.