The rig was conducting a scheduled Well Control / H2S drill. All personnel had donned self-contained breathing apparatus (SCBAs), had mustered and were preparing to debrief. At that time there was an announcement over the intercom: “There is a fire in the galley, this is not a drill.” Fire Fighting (FF) crews were mobilized to combat the fire. Power to the galley was shut off. Because of the amount of smoke in the galley it was difficult to determine the source. Investigation revealed the deep fat fryer as the fire’s source. CO2 and dry chemical extinguishers were used to put out the fire, and a FF crew was standing by with fire hose. The fire in the fryer was extinguished, but fire was discovered in the vent above the stove and fryer which was put out with a fire hose. Another crew closed off the vent which helped to extinguish the fire.