The oxidation kinetics of Fe2+ ions to Fe3+ in concentrated H2SO4-FeSO4 solutions was studied with isothermal and isobaric experiments carried out in a laboratory-scale pressurized autoclave. The experiments were performed at temperatures between 60 and 130 degrees C and oxygen pressures between 4 and 10 bar. The kinetic results revealed that the oxidation rate increases with temperature and pressure. A rate equation was derived for the oxidation process, based on the assumption that stepwise complexation of Fe2+ with dissolved oxygen is rate determining. The rate equation has the form r = a(1)c(Fell)(2)c(o)/(1 + a'c(Fell)), where c(Fell) and c(o) are the concentrations of Fe2+ ions and dissolved oxygen, respectively a(1) and a' are experimentally determined kinetic parameters. A comparison of the experimental data with the model fit revealed that the proposed rate equation is applicable for the prediction of the Fe2+-oxidation kinetics in acidic solutions.