Gulf-oil studies stalled by scarce samples, Nature.com, January 14, 2011:
Ira Leifer, an oil-spill expert at the University of California, Santa Barbara, was part of the US-government-led task force that produced the official flow-rate estimate for the spill. He began requesting [oil] samples within days of the initial blowout for work to support efforts to improve remote sensing of surface oil, but eventually gave up. ...
Working as a representative of the government, Leifer originally thought that getting samples would be relatively easy.
"But it didn't work that way," he says. "At the time it was unclear exactly how much was by design and how much was due to the chaotic nature of the response. However, the pattern repeated itself."
He thinks that similar to BP's apparent reluctance to release video footage of the spill early on, the lack of sample distribution could be a tactic aimed at minimizing the information ultimately available on spill impacts.