Halliburton Energy Services, Inc. general counsel Albert Cornelison’s headaches escalated to migraine level last week as the presidential oil spill commission said preliminary testing showed that the company found repeated problems with the cement it was planning to install in BP PLC‘s doomed oil well but used it anyway.

The commission’s chief counsel, Fred Bartlit, Jr., wrote in an Oct. 28 letter to commissioners that Halliburton knew its cement was unstable prior to the explosion aboard the Deepwater Horizon oil rig that killed 11 workers and set off the worst offshore oil spill in U.S. history.