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.

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.

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.)