I believe it was March 22, 2005.  

and HOs was the first substantive post:

http://www.theoildrum.com/classic/2005/03/oil-price-changes.html

Um! I actually think it was the Micawber post (which we later reposted with a different date stamp). (Hence the reference to sixpence).

But that is merely a quibble, as it has been a joy to watch the site grow, and the depth of posts and comments broaden as much as it has.

Thanks everyone, but particularly Prof and Super G, 'cos they're the ones who have really built the foundation that has got us here today.

HO