Abstract: Monitoring and fault diagnosis of power transformers has always drawn the attention of all utilities worldwide. It has become important to detect the incipient fault of a power transformer at an early stage, diagnose properly and also to provide the remedies. Dissolved Gas Analyses (DGA) is widely used to detect incipient faults in oil filled power transformers. Various methods are used to interpret DGA results i.e., C.E.G.B. Rogers’s ratio, IEC and IEEE ratio codes: Rogers, Dernenburg and Duval triangle methods. In this study, a relationship between the formations of hydrocarbon gases and the specific temperature and their solubility has been presented. For this study, more than couple of 100s of faulty transformer DGA sample reports from the different utilities in India (>10 years) with fault interpretation by different methods are collected. Against the same reports the Duval triangle, a graphical manual and software (MATLAB-7.4) are crossed compared.