Dissolved gas analysis (DGA) is a diagnostic tool that used to detect the incipient faults of power transformers through the correlation between the content of gases dissolved in transformers oil and a particular malfunction. The early detection of incipient faults in power transformers reduces costly unplanned outages. Some classical methods that depend on gases concentration in transformers oils are used to interpret transformer faults such as Dornenburg, Rogers, Duval triangle and key gases methods. These methods in some cases did not give the same results; therefore, an expertise method is developed to give the fault type according to the dissolved gases concentration in oil. A software code is designed using logic functions to get the type of the faults in transformers. The age of transformer is taken into account in our calculations. The results from the software code illustrate the program reliability as an early detection tool of transformer faults. Key words: Dissolved gases analysis- transformer oil- interpretation of transformer faults.