Rapid, introductory analysis of gases dissolved in insulating oil (DGA) carried out in the field can help in effective screening of faulty transformers as well as minimising number of classical laboratory chromatographic DGA tests. It is also crucial for shortening a time gap between oil sampling and its analysis. A novel approach to DGA is presented in this paper. A rapid analysis of oil samples is carried out by means of a portable analyser fitted with electrochemical gas sensors. Extraction of gases from the oil matrix is achieved by means of a dynamic, closed-loop stripping process. The analyser, which was built, is controlled by a microprocessor and may be operated in the field as an autonomous device. The system incorporates only two gas sensors and due to an extended set of their output signal wave descriptors used for the analysis it allows for a reliable identification of fault gases present in an oil sample. The identification of basic transformer fault types is illustrated on the basis of analytical results obtained for artificial oil samples prepared in a laboratory as well as those taken from transformers in-operation.