WASHINGTON The causes of the massive Gulf oil spill will be laid out for the first time today by investigators working for President Barack Obama’s independent commission, potentially shifting the blame and settling disputes between companies over the largest offshore oil spill in U.S. history.

Representatives of the three companies most involved in the April accident Halliburton, Transocean and BP will be on hand to answer the allegations and respond to questions.

“It’s the first public look at the events and actions that our investigators believe contributed to the blowout,” said David Cohen, a spokesman for the seven-member commission, which has a Jan. 11 deadline to deliver a report to Obama outlining what caused the disaster and what needs to be done to prevent another one.

In a preview of what is likely to come, the panel’s chief investigator, Fred H. Bartlit Jr., revealed in a letter last month that testing on cement mixtures similar to those used in the well showed that the formula was unstable before the blowout, but BP and Halliburton used it anyway. Bartlit said the companies should have reconsidered the type of cement used in the well. Cement is an essential barrier to preventing blowouts.

Hours after the letter’s release, Halliburton Co., the contractor hired by BP to mix and pump cement, said in a statement that it never conducted stability tests on the final mixture, and the earlier failed tests were on a different formulation than the one used.

After months of hearings, investigations and finger-pointing, there is still disagreement over what and whose mistakes triggered the explosion that killed 11 workers and released more than 200 million gallons of crude oil from BP’s Gulf of Mexico well.

The president’s commission could bring needed clarity as the first independent body to weigh in. Other investigations have been done by companies involved in the blast, Democratic lawmakers keen on taking on Big Oil and boards with members from the government agency that approved BP’s drilling plan.

BP even questioned how its own employees misread a critical pressure test before the blowout.