Well, the most light aluminum Fueltank on a serial-Bike, as far as I remember, was the Fueltank of a Honda RC30. Not sure anymore if maybe the Yamaha OW02 Fueltank was at less weight.

However, close to all Fueltanks of modern Sportsbikes are damn heavy, and sometimes even a bit lttle Capacity for a Roadbike, and way not enough for WSBK or Andurance Racing. The usual fueltank is made from mild steel and weights approx (6.5kg) 14,3 lbs, but even the Plastic-Fueltank of a Ducati 1098 is at the same weight, and still the new 2010 Aluminum Fueltank for the 1098 is at 5.2 kg- so 11.47 lbs. The Desmosedici Aluminum Fueltank is at 14.3 lbs too, and only 15 liters Capacity.

How does a 22 Liter Aluminum Fueltank with only 2.35 kg - or 5.58 lbs sound ?

Impossible ? No. It's just to use 1mm Wall-thickness Aluminum sheet Metal and CNC machined molds - and you need a Welder with incredible Skills. That's it, the recipe for very light Aluminum fueltanks, which are at the same Weight to Capacity Ratio as WSBK or Moto GP Fueltanks!

Aluminum Fueltanks for most modern Sportsbikes now available, close to the weight of Carbon Fueltanks, without the safety-downside of Carbon fueltanks- and: increased Capacity !