It's based on current consumption levels. However, there are a couple of things to consider. Domestic consumption, for instance, has dropped in the last eight years by well over 10% because we've become more and more efficient in our use of natural gas. Countering the prospect of more market share is the reality of more efficient use. Those don't balance completely evenly, but that is part of the calculus. The assumption is on the basis of current market share.
We're always somewhat cautious when we talk about how much prospective gas there is. When we used to say there was 30 years of gas, we would say that every year. We'd say it every year because more and more of the resource is identified and then more reserves are created. There's a difference between reserves and resources.
As the market price changes up and down, there is more work done on identifying resource and the picture continues to improve. I suspect that in ten years we will still say it will be 100 years. Even if demand continues to go up, I think we'll still be saying it. It's because as demand increases and prices change, producers respond and new resources are identified. The fundamental story is that there is an incredible amount of the resource available.
The last point I'd make is that we talk about conventional resources. Those are the ones we've been using for a long time. The unconventional resources are the shales, the tight gases, the coalbed methanes we've started to recover more recently.
Then there's a third resource base, which is hydrates. We don't even talk about hydrates at this point, although there was an announcement a few weeks ago by the Secretary of Energy in the United States on the prospects for hydrates, and both the Japanese and the Norwegians are doing extensive work on it. The numbers on hydrates run into the hundreds and hundreds and hundreds of years.
Our concern is not on the resource side; it's on the use side.