If we get CNG will we run out, in America?

I'm all for this conversion, and will support writing to our senators, but I have to ask if we have enough CNG in America to support this incentive? Here is a website that gives 10 things to know about CNG conversions and it says in one of the answers, that we will end up importing natural gas, as our demand increases.

I know Pickens says we have enough to use in America, for at least 20 years, so why are there other calculations out there, that say we don't have enough. Will someone please post some answers on this question. Here is the website in question.
http://earth2tech.com/2008/07/09/10-things-you-should-know-about-natural-gas-vehicles/