Optimal operating conditions observed by peer reviewed publications for Fenton oxidation of raw and biological and coagulation treated leachates were reviewed and statistically analyzed. For the first-stage Fenton oxidation, the optimal pH range of 2.5-4.5 was observed for raw and coagulation treated leachates with a median pH of 3.0, whereas, for biologically treated leachate the optimum pH range was 2.5-6.0 with a median pH of 4.2. Theoretically, the optimal ratio of H(2)O(2)/Fe(2+) should be the ratio of rate constants of the reactions between OH() radical with Fe(2+) and H(2)O(2), which is approximately 11; however, for leachate treatment, a median optimum relative dose of 1.8 (w/w) (3.0M/M) was observed. Biologically treated leachate showed relatively lower optimum ratio of H(2)O(2)/Fe(2+) doses (median: 0.9 w/w) as compared to raw (median: 2.4 w/w) and coagulation treated (median: 2.8 w/w) leachate. Median absolute doses of H(2)O(2) and Fe(2+) were 1.2mg H(2)O(2)/mg of initial COD (COD(0)) and 0.9 mg Fe(2+)/mg COD(0), respectively and raw leachate required higher reagent doses compared to pretreated leachates. A universal Fenton oxidation relationship between COD removal efficiency (η) and COD loading factor (L(COD)) for landfill leachate treatment was developed. As L(COD) increases from 0.03 to 72.0, η varies linearly as η=0.733 L(COD)-0.182. This robust linear relationship between L(COD) and η holds for Fenton oxidation of raw as well as biological and coagulation treated leachates. The relationship was validated using Leave-one-out cross validation technique and errors in predicting η using L(COD) were evaluated by applying Monte Carlo Simulation. As a result, the relationship can be used as a universal equation to predict Fenton treatment efficiency for a given COD(0) loading in the range of 0.03-72.0 for landfill leachate treatment.