 About 4 percent of the CBM wells are completed in the Lower Cretaceous Mannville formation, at depths of to .Author David J. Hughes in his 2004 book entitled "North America's Natural Gas Crisis", predicted that the Western Canada Sedimentary Basin would likely continue to be the main gas supply area in Canada for many years, however, declining production and the likelihood that much of the gas will be diverted to fuel new oil sands plants mean that the probability of there being sufficient surplus gas to meet projected U.S. demand is low, and the US will have to look elsewhere for future gas supplies.The WCSB contains about 90 percent of Canada's usable coal resources.