True gas is sold by its energy content or per million BTU's but then we would have to discuss the fact that Prudhoe Bay gas has 12% CO2 in it that has to be removed before you can sell it.  The average reader would get confused so its easier to say that natural gas is sold on the basis of 1,000 cubic feet so 200 trillion is 200 billion when its sold.  Its just like when people say Asian spot LNG is close to $9 but they fail to mention a meg Australian LNG plant is down due to a technical issue so spot prices have risen.  When the plant goes back on line the price will drop.