Powdered Fe2O3, (1:4 w/w) V2O5-[(2:1 w/w) MgO-Al2O3], and Fe3O4, 5-80 mg (s(o)) each, were studied by TPR using 5-60 mL/min (F) of (5:95 v/v) H-2-Ar (c(o) = 5 vol.% H-2) over 373-1473 K (b = 5-20 K/min) so as to keep (except for Fe2O3) K = s(o)/(F(.)c(o)) and P = (b(.)s(o))/(F(.)c(o)) within 55-140 s and 0-60 K, resp. These criteria introduced for single-stage reductions were found to be applicable, preferably P, to multi-stage reductions. However, even at constant P and K, peak temperatures and half-widths were strongly dependent on b, s(o), c(o), and F. Metal oxide reducibility comparisons based on peak temperatures were incorrect and the constancy of P or K was inconclusive. The K-criterion is correct only for isothermal reduction in hydrogen flow.