In this paper, the diameter of the pipe necessary for the lubrication oil to be entrained in the sucking and discharge line of the refrigerating systems using various alternative refrigerants calculated, its change range in accordance with temperature has been studied. The values of the minimum velocity of the refrigerant (Vr,min) and the minimum refrigeration load (qr,min) necessary for the oil in the pipes in the suction and discharge lines to be entrained in accordance with the estimated pipe diameters determined at the first stage of this study have been calculated, and the diameters of the pipes to be used in the light of these values have been calculated. In a refrigeration system in which refrigerating load is 1 kw for copper pipes of K and L type, eco-friendly, alternative R134A, R410A and R423A refrigerants in place of refrigerants detrimental to ozone layer and leading to global warming have been used. [ABSTRACT FROM AUTHOR]