I just saw this interesting story indicating that there has been a second – albeit smaller – oil spill on the Gulf, dating back to April 30. This second leak is coming from a nearby drilling rig, the Ocean Saratoga. From the Mobile Press-Register:
A nearby drilling rig, the Ocean Saratoga, has been leaking since at least April 30, according to a federal document. While the leak is decidedly smaller than the Deepwater Horizon spill, a 10-mile-long slick emanating from the Ocean Saratoga is visible from space in multiple images gathered by Skytruth.org, which monitors environmental problems using satellites. Federal officials did not immediately respond when asked about the size of the leak, how long it had been flowing, or whether it was possible to plug it….Saturday, the Southwings environmental group flew over the Ocean Saratoga with photographer J. Henry Fair of Industrial Scars.com and returned with photos that appear to show a large oil crew boat pumping dispersants into the water at the spill site….Officials at the National Response Center said that the spill had been reported, but would not say when it began.
A serious question, as the article points out, is what we'd learn if we systematically tracked the performance of these wells.
Looks like there might actually be two other spills – the one you mentioned and then another from "Platform 23051." http://motherjones.com/blue-marble/2010/06/two-more-gulf-spills