Halliburton Co. is pushing back against the presidential oil spill commission's findings outlined yesterday that the company knew its cement mixture was unstable months before the accident.

In a sharply worded rebuttal issued late last night, the company said its cement job was not to blame for the blowout at the ill-fated BP PLC well.

The company, which BP contracted to cement portions of the well, points the finger back at BP, saying it cut corners and skipped crucial tests that would have indicated problems with Halliburton's cement.

At issue is a letter sent yesterday to the seven-member panel appointed by the president to probe the causes of the oil spill by the commission's lead investigator. The report cites documents from Halliburton that show the company knew the results of three separate laboratory tests on the cement that showed the mixture did not meet industry standards.

Only one test conducted before cement was pumped down the wellbore showed the cement would behave as predicted, the letter says. And "we are not yet certain ... whether the test was even complete prior to the time the cement job was poured at the Macondo well," the letter says (E&ENews PM, Oct. 28).

The letter also adds that BP knew the results of at least one of the tests in March, but Halliburton may not have highlighted the significance of the cement testing data.

Halliburton is challenging the accusations, saying the first three tests on the cement were either preliminary or irrelevant and that BP was aware of the results of all the testing before cementing began.

The company adds that BP instructed Halliburton to change the cement composition following the final successful test but did not order full testing on the new formula.

Halliburton says BP should have conducted a cement bond log test, a procedure that evaluates the integrity of the cement.

"BP, as the well owner and operator, decided not to run a cement bond log test even though the appropriate personnel and equipment were on the rig and available to run that test," Halliburton said in the statement.

Halliburton is also challenging the panel's findings from simulated cement tests. The panel commissioned Chevron Corp. to test samples of cement chemically identical to the cement used on the Macondo well. Those tests also found the cement was unstable.

But Halliburton says the results of the simulated tests are skewed because they did not use the same batch of cement that Halliburton used at the well site.

"Halliburton believes that significant differences between its internal cement tests and the commission's test results may be due to differences in the cement materials tested," the statement says. "The commission tested off-the-shelf cement and additives, whereas Halliburton tested the unique blend of cement and additives that existed on the rig at the time Halliburton's tests were conducted."

One of the Chevron experts who conducted the simulated tests is expected to testify before the panel next month to explain the findings. Halliburton is already running damage control.

"Halliburton believes further comment on Chevron's tests is premature and should await careful study and understanding of the tests by Halliburton and other industry experts," the statement says.

A federal judge this week ordered Halliburton to turn over cement and materials used on the Deepwater Horizon project to federal investigators from the Interior Department and the U.S. Coast Guard.

Reporter Lawrence Hurley contributed.