An equation suitable for analyzing the high-temperature oxidation kinetics of metals in the case where scale volatilization is inevitable is presented. The equation derived Delta m = k(p)'(1/2) t(1/2) - (2/3 + f(Me)/3) k(nu)'t, where k(p)' is the parabolic rate constant, f(Me) the mass fraction of the metal Me in the scale oxide MenuO, and k(nu)' the volatilization rate constant of the oxide, has such a simple form as to be used for easily separating the mass gain into the scale growth due to diffusion and its volatilization by curve-fitting the equation for mass gain data. The limitations of the application of this equation are discussed, and its validity is verified by its application to experimental data reported for Cr2O3-forming alloys.