Spontaneous combustion is an inherent problem to the coal mining industry. The paper describes an electrochemical method called wet oxidation potential technique for determining the susceptibility of coal to spontaneous combustion. Altogether 78 coal samples collected from thirteen mining companies spreading over most of the Indian Coalfields have been used for this experimental investigation and 936 experiments have been carried out by varying different experimental conditions to standardize wet oxidation potential method for wider application. The results of wet oxidation potential (WOP) method have been correlated with the intrinsic properties of coal by carrying out proximate, ultimate and petrographic analyses of the coal samples. Experimental results are first analyzed with principal components analysis and then by multiple regression analysis. Results obtained from this method have been compared with one of the widely used method, i.e. crossing point temperature (CPT) in India. The experimental investigation clearly indicates that WOP method with 0.2 N KMnO4 in 1 N KOH solution at 45 degrees C (susceptibility index PD12) should be used for finding out the susceptibility of coal to spontaneous combustion. PD12 results are well corroborated with CPT results. (C) 2014 Elsevier B.V. All rights reserved.