David Gouldin, the Asia-Pacific operations manager at Atlas Drilling which operated the West Atlas rig, told the commission of inquiry into the spill a whiteboard in the drilling supervisor's office had the installation of the larger 13 3/8-inch pressure cap noted as an "outstanding job", but the supervisor said he had no recollection of whether the job had been ticked off as completed.

He agreed that a whiteboard was an inadequate system to ensure verification of jobs done, adding there were "shortcomings" in the process under which both PTTEP and Atlas Drilling had to agree and sign off in writing on major milestones.

Gouldin also agreed several times with counsel assisting the inquiry, Tom Howe, that some engineering work carried out on the rig was not in line with "good oilfield practice" and the failure to do detailed checks of a cement casing shoe and the absence of caps meant there were no properly tested barriers.

The inquiry was told the failure to install the bigger cap led to corrosion of casing threads down the well, which in turn led to the removal of the smaller cap, leaving the well vulnerable to blowout.

When questioned, Gouldin agreed the proper supervision of barrier installations should involve someone with sufficient expertise to recognise problems but that was not the case on the Atlas rig.

Meanwhile, Atlas Drilling rig manager Donald Millar said he should have picked up from a daily drilling report that cementing work done in March 2009, six months before the blowout, had failed.

The inquiry was told a cement "shoe" for the well was improperly poured, with "floats" failing during the job and seawater leaking in.

Millar agreed a remedial step of pumping back an additional amount of cement and fluid after the floats failed had likely worsened the situation.

"I didn't recognise the significance of it," he said.

Millar also admitted he did not have enough expertise to recognise the problem.

"If I had recognised the significance of it, I would have put the calculator on it. I would have perhaps picked up and mentioned something.

"I didn't recognise the ramifications of that back flow and the re-injection of it."

He added that on reviewing the data, he was also "astonished" to learn a pressure control cap had not been installed on the well.

The inquiry will hear from Seadrill and PTTEP staff and Northern Territory Department of Resources officers during two weeks of hearings.

The H1 blew out in August last year and continued to spill oil and gas into the Timor Sea until operations to plug it finally succeeded in November.

A fire broke out while heavy mud was being pumped into the well to stop the leak, also leading to the write-off of the West Atlas.