Another oil rig in the Gulf of Mexico exploded today. All crew members survived. Right now, nobody knows whether or not the explosion caused a leak in any of the seven wells that the rig collects from. There have been reports of an oil slick on the water near the fire, but that could just as easily be from the finite amount of oil stored on the rig—which would still a spill, but a significantly less problematic one.
Other than that, there's not really much information out about this right now. If anybody's learned anything from Deepwater Horizon it seems to be that you're better off, PR-wise, if you don't have to correct everything you say two days later.
To give you something to chew over in the meantime, though, Deep Sea News has been doing a really interesting series on the science (such as it is) of oil dispersants. It's interesting, not just because of the basic facts, but also because it gets into the details of why we don't know more.
Dispersants must be applied successfully and have a high effectiveness once in ocean waters. This sounds easy, in principle–once you've perfected your Corexit formula in the lab, just spray it from a helicopter, and voila! Except there are a lot of factors which you also have to take into account: the composition of the oil spilled, sea energy, whether the oil has been subjected to weathering at all, exact type of dispersant used and the amount which you sprayed, and ocean temperature/salinity.
Thank goodness for all those lab tests over the years which figured all this stuff out, you say. Um, well actually it seems like even designing simulation experiments is difficult, and different tests can report different effectiveness scores for the same dispersant. It is difficult to accurately scale up lab tests in order to predict dispersant action on real spills. Older studies used methods and analyses which have since been discredited. Wave-tank tests can probably provide upper limits on dispersant effectiveness, but there are SEVENTEEN (!!) critical factors that require strict control for accurate results (Fingas 2002). Field tests in open ecosystems are even worse for measuring the fate of oil and controlling variables. In terms of measuring dispersant effectiveness, tank tests, field tests, and lab tests all disagree. Awesome.
Part 2: How toxic are dispersants?