Simple measurements of H2O2 concentration or CO2 evolution were used to evaluate the effectiveness of the use of Fenton's reagent to mineralize organic compounds in water and soil contaminated by crude petroleum. This methodology is suitable for application in small treatment and remediation facilities. Reagent concentrations of H2O2 and Fe2+ were found to influence the reaction time and temperature, as well as the degree of mineralization and biodegradability of the sample contaminants. Some H2O2/Fe2+ combinations (H2O2 greater than 10% and Fe2+ greater than 50 mM) resulted in a strong exothermic reaction, which causes peroxide degradation and violent gas liberation. Up to 75 % TOC removal efficiency was attained in water and 70% in soil when high H2O2 (20%) and low Fe2+ (1 mM) concentrations were used. Besides increasing the degree of mineralization, the Fenton's reaction enhances the biodegradability of petroleum compounds (BOD5/COD ratios) by a factor of up to 3.8 for contaminated samples of both water and soil. Our experiments showed that low reagent concentrations (1% H2O2 and 1 mM Fe2+) were sufficient to start the degradation process, which could be continued using microorganisms. This leads to a decrease in reagent costs in the treatment of petroleum-contaminated water and soil samples. The simple measurements of H2O2 concentration or CO2 evolution were effective to evaluate the Fenton's reaction efficiency. (c) 2007 Elsevier B.V. All rights reserved.