In this study, Fenton oxidation and activated persulfate oxidation were used to investigate the optimized in situ chemical oxidation (ISCO) process for its efficiency on petroleum-hydrocarbon contaminated groundwater cleanup. In the batch and column experiments using benzene and toluene as the target compounds, oxidant depletion, soil oxidant demand (SOD), adsorption of oxidant on soils, and oxidation kinetics were studied. Results show that Fenton oxidation process was more catalytic than activated persulfate oxidation by ferrous iron catalysis. Higher SOD value was obtained for H2O2 than persulfate because H2O2 had higher reactivity to soil organic matter. In addition, increased benzene and toluene oxidation rates were observed with increased concentrations of H2O2 and persulfate oxidants. The calculated pseudo first-order decay rate constants (k') for Fenton and activated persulfate oxidation processes were 1.65 and 0.13 1/h for benzene and 1.28 and 0.1 1/h for toluene, respectively. Compared to persulfate oxidation, results indicate that Fenton oxidation had much higher reaction rates on petroleum hydrocarbon oxidation. Results from the column experiment show that up to 5.94 pore volumes (PVs) of H2O2 solution and 12.85 PVs of persulfate solution were required to cleanup benzene and toluene contaminated groundwater with an oxidant concentration of 10 wt%, ferrous iron concentration of 100 mg/L, and initial contaminant concentration of 50 mg/L. Results indicate that the Fenton oxidation process would be a more practical and efficient approach to remediate petroleum-hydrocarbon contaminated groundwater. The results would be useful in developing an ISCO system for a practical field application to cleanup benzene and toluene contaminated groundwater. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.