The Coast Guard told media this morning that BP’s diamond-edged saw has become stuck trying to cut through the riser pipe at the top of the blowout protector (BOP). That means the effort to "cut, cap and capture," the oil gushing out the top is stalled until they solve that problem. [Update: early afternoon videofeed appears to show a giant saw being moved apart from the BOP -- a replacement saw, or (per CNN) the original being sent up for repairs?]

Update II, 4:00 p.m. Eastern: Folks at The Oil Drum are now claiming the Coast Guard and BP report the blade has been freed up. CNN agrees, says saw was sent up for repairs.
5:30 p.m. NYT says BP now thinks the retrieved saw has become "ineffective." They’re searching for alternatives.]

Update III, 10:00 p.m.: Per CNN and Oil Drum, Adm. Allen reports they’re going to try the same saw shear they used on the lower riser cut; the diamond wire cutter is out.

From the Washington Post:

The latest attempt at containing oil spilling into the Gulf of Mexico — a plan to saw off a leaking pipe and slide a cap over it — has been stopped because the saw is stuck, a Coast Guard official said Wednesday morning.

Adm. Thad W. Allen, who is in charge of the response to the massive deep-sea spill, said a "diamond-wire" saw had become hung up on the pipe it was supposed to cut. He said that crews using remotely driven submarines were trying to get it loose but that the solution might be to bring in another saw.

Allen said he would know more Wednesday afternoon.

"Anyone who’s ever used a saw knows it can bind up," Allen told a news conference.

Uh, yeah, lots of people understand this problem. Loggers and craftsmen who have to cut very big or hard stuff deal with it everyday. And anyone who’s ever cut a heavy board quickly learns you have to position the board on the supports so that as the cut progresses, the forces (e.g., gravity) affecting each side of the cut don’t push the sides together and trap the saw. If the thing you’re cutting can’t be moved, you position the saw blade to solve the same problem. And it you can’t position the board or saw for that, you have to keep widening the cut as you go, to keep the saw from binding.

There’s probably a reason they chose to cut from the direction they’re using, but I haven’t seen an explanation. I’ve been wondering why they started cutting from what appears to be a side of the riser/BOP close to the bent-over portion of the riser instead of the side opposite the riser bend, so gravity working on the riser bending it down slightly might eventually work to widen the cut gap as they got closer to the end.

Perhaps that was the eventual plan as they progressed, or maybe this doesn’t matter here; there are other factors at work. But they apparently didn’t anticipate whatever forces are working to grab the saw blades as they got deeper in the cut, and we probably won’t know what happened unless/until this effort fails.

As noted in the comments, a more difficult problem is the drill pipe inside the riser; if that pipe can move around inside the riser, rather than hold steady, then the saw blade would have a tough time cutting it without jamming.

In the meantime, the worsening fate of the Gulf depends on a saw blade stuck in a large bent pipe, 5000 feet deep in the ocean.