http://fireaviation.com/2017/01/09/747-air-tanker-receives-federal-approval/The 747 SuperTanker has received interim approval from the Interagency Airtanker Board (IAB) on January 6, 2017
The 747 can hold 19,200 gallons, much more than any other air tanker.
For comparison, the DC-10 very large air tanker carries 11,600 gallons, while the BAe-146, RJ85, and C-130 hold up to 3,000 to 3,500 gallons. The P2V Korean War vintage aircraft that has been the workhorse air tanker for decades usually carries less than 2,000 gallons. The S-2T used by CAL FIRE holds up to 1,200 gallons.