BP has demanded that a court allow a huge forensic examination of Halliburton's IT systems, over accusations that the US cementing contractor is hiding evidence into the Gulf of Mexico oil spill.
The demands come in a 310-page motion filed by BP in a Houston court, as part of its £24 billion series of lawsuits against Halliburton, rig owner Transocean, and blowout preventer manufacturer Cameron.
BP has said safety systems failed and key technology on the rig was "unreasonably dangerous". It blamed Halliburton for failing to properly use its own OptiCem modelling software to analyse safe drilling conditions.
The spill in April 2010 killed eleven oil rig workers and led to millions of barrels of oil spilling into the sea. US government reports have concluded numerous factors caused the accident, and blamed BP and its contractors.
BP has accused Halliburton of deleting from computers the key cement modelling data used to analyse the slurry mix needed at the Macondo well. Halliburton denies the claims and has said the motion is "without merit".
BP asked a judge to penalise Halliburton for the issue, and to appoint a team of forensic experts to trawl through Halliburton's systems.
Such an investigation would likely even assess Halliburton's more basic IT systems, including standard PCs, and involve a vast email trawl.
Halliburton cement expert Rickey Morgan has already said in court depositions that he "didn't want to put anything on an email that could be twisted, and turned", and that as a result he had limited what he wrote to bosses.
A similar trawl by US authorities on BP computers produced revealing emails that showed BP engineers taking a time-saving decision on the amount of safety cement supports used for the well drilling at the disaster site, before the accident happened.
US government investigations established that BP failed to fully adhere to the results of the OptiCem software, which demanded 21 centralisers be used. BP initially adhered to the software tests and ordered 15 extra centralisers, in addition to the six in place. But when technicians on the rig received the extra centralisers they mistakenly decided they were the incorrect type. At this point BP proceeded with the drilling anyway, with the six centralisers, in order to avoid millions of pounds being spent on unused drilling days.
As the drilling proceeded on six centralisers, Brian Morel, drilling engineer at BP, wrote an email to colleague Brett Cocales, saying: "Who cares, it's done, end of story, we'll probably be fine".
The OptiCem software has been an area of focus of many of the reports that have followed the spill.
While US authorities concluded that BP failed to adhere to the software results, the oil firm has accused Halliburton of "failing to properly run the OptiCem model, including failing to make the proper assumptions" and inputting "demonstrably wrong data". Halliburton denies the charges.
BP has equally accused rig owner Transocean of failing to use advanced monitoring screens to properly watch the well conditions, and manufacturer Cameron of not designing a proper blowout preventer, the key device that plugs the well. Transocean and Cameron have insisted the devices were safe and well managed on their part.