BP investigators, faced with questions about their report on the causes of the Deepwater Horizon disaster, acknowledged Sunday before a panel of engineering experts that their report had limitations.

"It is clear that you could go further into the analysis," the report's chief investigator, Mark Bly, who was head of BP's safety and operations. "This does not represent a complete penetration into potentially deeper issues.” Bly called his team’s report “a good foundation for further work.”

Here’s what The Washington Post noted about how the report was produced:

Conclusions were made without examining the drilling rig, which remains on the sea floor, or the blowout preventer, a key safety device that was brought to shore only recently. Instead, the company relied extensively on real-time data collected aboard the rig to reconstruct what happened. BP also did not have access to samples of the cement used to seal the well, and said Halliburton refused to supply a similar mix for testing. BP has said the cement failed.

The panel also questioned why BP left out other items from the report, including an analysis of possible organizational flaws and hiccups in the chain of command, as well as more information on the rig’s workers. The panel of experts—created jointly by the National Academy of Engineering and National Research Council—is investigating at the request of the Interior Department. 

The experts also questioned Halliburton on why it allowed BP to proceed, even though BP had installed only six of the recommended 21 centering devices before cementing. (Halliburton’s vice president of cementing, Thomas Roth, said the company “didn’t see it to be an unsafe operation as it was being executed,” and BP had the ultimate decision-making responsibility, Bloomberg reported.)

As we’ve noted, BP’s report emphasized the significance of decisions by others—primarily Halliburton—in its assessment of how the blowout began. The report also dismissed the role that BP's choice of well design played in the disaster and minimized BP's decision not to fully implement Halliburton recommendations in the run-up to the blowout. Some of the more interesting tidbits in the report, we’ve also noted, were buried in little-noticed appendices.

One panelist, Stanford geophysicist Mark Zoback, put forward another theory on the cause of the blowout, The Wall Street Journal reported. Zoback noted that the loss of fluid during cementing could have been because of cracks in the rock formations at the bottom of the well. 

“I'd like to just maintain the possibility that one reason that the cement job may have failed was because of fracking at the time of cementing,” Zoback said. According to the Journal, if Zoback’s theory is right, it would “undercut BP’s effort” to deflect criticism of its well design.

In the hearing, BP stood by its design choice. Kent Corser, a drilling engineer manager with BP, told the panel that its well had “a robust design”; Roth, of Halliburton, said that the design had “compromised well integrity.”

The panel is expected to issue a preliminary report before the end of October, and a final report by the end of the year.