The corresponding states and extended corresponding states principles have been evaluated for refrigerants. In the two corresponding states techniques the Riedel and Wagner vapour pressure correlations have been used to express the vapour pressure for the reference fluids. As reference fluids CFC12 and HFC134a have been used. These two fluids cover the acentric factor interval wherein refrigerants are found. Parameters have been estimated for CFC12 and HFC134a according to the Reidel and Wagner vapour pressure correlations used in the extended corresponding states principle. Experimental vapour pressure data for CFC12 and HFC134a have been used to estimate parameters according to Riedel and Wagner used in the hypothetical fluid and deviation function used in the corresponding states principle.