"Only half a decade ago it looked as though the world might have only 50 or 60 years-worth of gas. Now shale and other unconventional as well as new conventional gas finds have increased that period to 200 years or more, by some estimates."
Who's estimates? I notice the article doesn't mention. Personally, I tend to stick to estimates from the likes of BP and Exxon, since I figure they know what they're talking about.