Vaisala. Dissolved gas analysis (DGA) is the only way to detect a range of internal faults in transformers. Although it is not an exact science, evaluation and interpretation based on statistics has been used for transformer condition assessment for decades. Online DGA monitoring has been available since the late 1990s and there are now various online gas monitors on the market each with their own technical specification, making it challenging for transformer owners to compare and evaluate the different options. To make the field even more complicated for utilities, laboratory DGA plays a role too. This paper describes various factors to consider when examining a monitor’s technical specifications and evaluating its performance, especially against laboratory DGA results. The main challenge is that there is not any explicit international reference available for DGA.