I first saw this piece on a huge oil discovery in North Dakota a little while ago, but didn’t pay much attention, since I’d never heard of Next Energy News before. Now that piece is making the rounds of the blogosphere (Rand Simberg, Instapundit) and one of Simberg’s commenters points to this post, which strikes me as credible. (As the very least, it has lots of supporting links.)
If this pans out, the upshot is 100–300 billion barrels of oil in the Williston Basin, which spans the U.S.-Canada border (with the largest portions being in North Dakota and Saskatchewan). By comparison, Saudi Arabia has 260 billion barrels in proven oil reserves.
UPDATE (5/20): For some reason, a lot of people are finding this post through search engines. Here’s my latest post on the topic.