Here is a few pictures I have received by E-mail from the burning and sinking of the MODU Deepwater Horizon:
Looking at pics #2 the rig was working in DP Mode, not moored by anchors.
(Yes, it is possible to do that in 5000 ft. water depth)
They had already completed drilling the well and was in completing and plugging the well for future development as a producer.
The BOP was still on the seabed so the flow of well fluid would have been shut in when the rig sunk, thus limiting the oil pollution.
Diesel Oil is far less of a problem in the warm waters of the Gulf, even if all 2.600 Cbm of it should leak out. (Assuming the figures in the press is right)
This is likely to renew the resistance against offshore drilling in US waters, I should think. Invest in Windmills, Solar and Nuclear.