Experimental results of the high-pressure phase behaviour for {xCHF(3) + (1 - x)H2O) and {x(1)CHF(3) + x(2)NaCl + (1 - x(1) -x(2))H2O} are presented. (Gas + gas) equilibria for five compositions with x(CHF3) (0.0334 +/- 0.0002)< x < (0.1389 +/- 0.0002) as well as for six compositions with x(1)(CHF3) (0.0305 +/- 0.0002) < x(1) < (0.1096 +/- 0.0002), and mole fractions x(2)(NaCl) (0.0046 +/- 0.0002) < x(2) < (0.0100 +/- 0.0002) were measured in a high-pressure autoclave equipped with sapphire windows and magnetic stirring. The phase transitions were determined visually. The pressure ranged from 20 MPa to 200 MPa, and the temperature from T = 470 K to T = 625 K. The (xCHF(3) + (1 - x)H2O} exhibits a type-III fluid phase behaviour without (gas + gas) immiscibility of the first kind. Isopleths for NaCl mass fractions omega = (0.01677 and 0.03336) relative to H2O are shifted towards higher temperatures compared with the binary mixture {xCHF(3) + (1 - x)H2O). In this system the temperature shift is more pronounced than for isopleths in the system (xCF(4) + (1 - x)H2O} upon NaCl addition. The objective of this study was to investigate the phase behaviour of model-systems encountered in supercritical water oxidation processes.