What the numbers mean is that we have more refining capacity than we need to supply our domestic needs. So, we import the crude oil, refine it, use almost all of it, and sell a percentage of it to the rest of the world. The biggest surpluses are in "unfinished oils" and "motor gasoline blending components." Mexico's rising petroleum product use is a big part of the story, as you can see in the by-country net import numbers.
So, the Journal's story is good news, in a general sense, but let's not make it bigger than it is. We're still buying massive amounts of crude oil from other countries. Take a look at Atlantic alum Matt Yglesias' post for a quick economic analysis.
This article available online at:
http://www.theatlantic.com/technology/archive/2011/11/is-the-usreally-a-net-petroleum-exporter-no/249269/