In a matter of moments, carbon-offset outfit TerraPass will be announcing a partnership with Expedia, the online travel site. The deal is, when folks book their flights through Expedia, they’ll have a chance during the checkout process to offset (their share of) their flight’s emissions. Short flights will go for $5.99, longer cross-country flights for $16.99, and international flights (13,000 miles or more) for $29.99.

This is a cool deal that I think will do a lot to break the offsets market out of its niche status. Right now, energy users have to initiate the process — go to terrapass.com and calculate their own offsets. That’s inherently limiting.

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Now, it’s just another part of booking travel. I’ll bet dimes to dollars that other online travel sites will be doing this same thing within a year.

Incidentally, for those of you who like to reward virtuous business practices, TerraPass’s Tom Arnold tells me that this is one of the first steps in a process whereby Expedia hopes to become a full-on green travel site.

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Oh, hey, look. There’s a post about the deal just now on the TerraPass blog. Check that out for more info.

(And yes, this really is my last post. Now I’m leaving for vacation. Really.)