The important parameters that have significant effects on the prediction of CHF (Critical Heat Flux) for R-12 (Dichlorodifluoromethane) were investigated. This was a preliminary study for a R-12 CHF correlation in uniformly heated vertical round tubes. Experimental data of Celata[1], Green and Stevens[2], Groenveld[3], Ilic[4], Katto[5], Merilo and Ahmad[6] and Stevens and Miles[7] were used for this analysis. Four representative CHF data sets at pressure condition of 9, 15, 19, and 27 bar were selected, analyzed, and compared to evaluate the effects other than the system pressure on the CHF were tube diameter (D), mass flux of water (G), and local true mass fraction of vapor (X_t). The results of this study have reaffirmed the feasibility that an advanced R-12 CHF correlation for uniformly heated vertical round tubes can be found.