The problems involved the well casing and the blowout preventer, which are considered critical pieces in the chain of events that led to the disaster on the rig.

The documents show that in March, after several weeks of problems on the rig, BP was struggling with a loss of “well control.” And as far back as 11 months ago, it was concerned about the well casing and the blowout preventer.

On June 22, for example, BP engineers expressed concerns that the metal casing the company wanted to use might collapse under high pressure.

“This would certainly be a worst-case scenario,” Mark E. Hafle, a senior drilling engineer at BP, warned in an internal report. “However, I have seen it happen so know it can occur.”

The company went ahead with the casing, but only after getting special permission from BP colleagues because it violated the company’s safety policies and design standards. The internal reports do not explain why the company allowed for an exception. BP documents released last week to The Times revealed that company officials knew the casing was the riskier of two options.