Sorry this is a long answer, but hopefully it's a descent answer.
In short; it's the whole planet and we're running out of the stuff, plain and simple.
There are complaints that people will make that - "it's the environmentalists", or "its a big plot" or some such, but there are two basic constraints.
1. Production - The oil production companies view the United States / North America as a "mature" marketplace, in that there are only 400 million "consumers" and the infrastructure to satisfy that marketplace exists already, and they simply see no need to build or expand upon their existing infrastructures.
Especially if it means "conforming" to any building or environmental safety rules or regulations, but eventually, the various refineries have been "maintained" such that no parts in the refineries are more than a few years old, and the production capacity fluctuates with the damage caused by storms, accidents or maintenance down-time.
Southern California/ Baja however hosts the newest terminal for LNG (liquified natural gas) which California has been developing for something close to 15 years now.
http://www.reuters.com/article/pressRelease/idUS171562+15-May-2008+MW20080515
2. Demand - WE (meaning the US) but also more broadly industrialized nations, use alot of the stuff.
Regarding oil itself, though, after the run-up in the last couple of years, a concerted effort to calm markets with talk of drilling offshore or where-ever, was calculated to bring the price down as the election nears, however, hurricanes don't respond to political pressure.
The real concern is the supply of the stuff is decreasing in spite of massive efforts globally to find more oil, anywhere we can.
The concept is called Peak Oil, and is well supported in the geological and broader market understanding of oil, and was discovered (although not embraced) by the oil companies themselves, in the 1950's, through the work of Dr. Hubbert.
http://en.wikipedia.org/wiki/Peak_oil or
http://en.wikipedia.org/wiki/Hubbert_peak_theory
Unfortunately, the finds that are being discovered are smaller and more remote each year. Before 1994, more exploration meant more finds and more production. So spend X amount of dollars and more or less get X amount of discoveries of new oil reserves, afterwards, two things happened.
1. Discovery rates plumetted and have never (and probably never will) increase again.
2. Production and USE continued to escalate beyond the new discovery rates.
This is called "overhang" and means that the clock is officially ticking, to a point where - likely - we will either have moved away from oil use, OR we will be market-shocked into reality, when the wells we currently use start to go dry.
http://www.planetforlife.com/oilcrisis/oilsituation.html
After 1994, oil exploration and production firms (Exxon, BP, Sinopec, Shell, coupled with firms like Halliburton, KBR, Fluor have all spend exponentially more money in exploration and come up zip), that SHOULD have caused our politicians and the American people, to stand upright and pay serious attention to conservation, alternative energy and other ways of being efficient.....but it didn't.
Here's a helpful site for more information from British Petroleum which is very slick but it is of course coming from an oil company
http://www.bp.com/productlanding.do?categoryId=6929&contentId=7044622
The EIA (a division of the Energy Department of the US Government) http://www.eia.doe.gov/ has some very good statistics about the issue.
And of course if you want to put a happy face on this whole mess, listen to Kris, http://www.youtube.com/kriscanshow
I read quite a bit about the issue a few years ago now and got a hybrid and live in a smaller apartment close to work, so my energy costs / use isn't that out of control. I suspect quite alot of people in the US will be doing the same in the next few years.
Books I recommend
1. The End of Oil : A really good examination of the how's, what's and why's of peak oil and the concern over time.
2. 1000 Barrels a second : A somewhat overly optimistic point of view from a market speculator, but a VERY good examination of this historical precedents for peak oil (in the wood, old-school hydro and whale-oil peaks of previous centuries).
3. Collapse - Jarred Diamond's examination of how relatively complex older civilizations failed to anticipate and plan, and how they failed because of those mistakes.
4. The Long Emergency - I personally don't recommend this wholeheartedly since It seemed overly dramatic and offered absolutely no solutions, but the author made several "predictions" which have since come to pass - so that kind of pisses me off - considering how pessimistic he is.
Someone else commented on Confessions of an Economic Hit Man, but having read the book and as compelling as I thought it might be, I got about 3/4ths of the way through (and did finish it), but realized there was not a single sourceable reference or footnote to such strident allegations, I would have appreciated something in that regard, like the book Imperial Hubris - which was compelling because it was so well sourced.