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In this article the results of an experimental study comparing gas generation in the natural ester transformer liquid FR3 and in the mineral oil Gemini X, under PD and sparking faults, are presented. The total amounts of fault gases were reported in microliters rather than in parts per million. The results show that the key gases generated under PD faults and under sparking faults are hydrogen and acetylene, in both Gemini X and FR3. This finding suggests that the conventional gas methods for diagnosing PD and sparking faults in mineral oil are also applicable to FR3. Although the total volume of fault gases under PD faults was more than 50 times higher in FR3 than in Gemini X, the total volume of fault gases per unit fault energy is similar for the two liquids. Thus it appears that the higher gas generation in FR3 is caused by the higher PD occurrence rate.