In our galley, we use LPG (Liquefied petroleum gas) to cook, by way of a gimballed stove.
The stove is fueled by a 5 kg (11 lbs) tank. pino houses two tanks with only one tank connected at a time, this way we can get a tank filled while the other is still in use. One 5 kg tank can last us two months, and less if we bake a lot.
We used to carry a 9 kg (20 lbs) tank, which could last us 4-5 months, but had to recycle it in japan.