BP Plc and its partners in the Gulf of Mexico oil spill have unleashed a $100 billion-plus barrage of legal claims against each other a year after the rig blast killed 11 workers and created an environmental disaster.

On the anniversary of the world's worst marine oil spill, BP filed lawsuits totaling more than $80 billion against Transocean Ltd and Halliburton Co.

And in a separate action on Wednesday, BP sued Houston-based Cameron International Corp, the maker of the blowout preventer, the so-called fail-safe device that neglected to automatically shut down the well.

BP is seeking up to the full cost of the disaster -- estimated at $42 billion -- plus costs, interest and punitive damages from each of the companies that helped it drill the doomed well.

Meanwhile, BP's partners in the well, Anadarko Petroleum Corp and Japan's Mitsui, filed a lawsuit against it, challenging BP's demands that they contribute to the cost of the clean-up effort.

Wednesday was the deadline -- one year after the disaster -- for companies connected to the spill to file claims against each other.

Analysts said the companies probably did not want the cases to ever get to court, as this would lead to a spectacle that would further damage their already battered images.

Instead, the suits were seen as tactical moves ahead of settlements that could see some of the burden shared. The litigation is expected to drag on for years.

It's got a fairly low chance of being successful, said one analyst who declined to be named because of the legal sensitivities around the case. I get the feeling that there is positioning going on here for a settlement.

So far, BP has met the full cost of the clean-up effort alone and is paying compensatory damages to those people in the Gulf area who were affected.

At midday, Transocean shares were off 2.2 percent, while BP shares in New York gained 0.3 percent. Halliburton shares slid 0.8 percent and Cameron shares were off 1.4 percent.

FRAUD ALLEGATION

BP said Halliburton concealed critical information that could have prevented the disaster.

Halliburton's improper conduct, errors and omissions, including fraud and concealment, caused and/or contributed to the Deepwater Horizon incident, BP said in a court filing.

Halliburton knew and understood it was misrepresenting material information, BP added.

Halliburton, which said it would vigorously defend itself against the claims, filed its own lawsuit against BP in Texas state court on Tuesday charging BP with failing to accept responsibility for the disaster, as called for in its contract.

The plain and unequivocal language of the contract requires BP to defend and indemnify (Halliburton) from virtually all claims arising out of the blowout, Halliburton said in its legal filing.

In January, the company disputed a U.S. presidential commission's characterization of its cementing work on the blown-out Macondo Well, saying that the report omitted key facts.

On Wednesday, BP also filed a lawsuit against rig operator Transocean.

FINGER POINTING

Since the outset of the disaster, BP has sought to blame its contractors, namely Transocean -- a move PR experts said had damaged its image. The presidential investigation into the report did criticize these companies, but directed most of its criticism at BP.

Service providers' contracts with operators usually provide indemnities against any environmental damage that may result from their work, and one analyst said this limited BP's opportunities to recoup cash from Transocean or Halliburton.

If BP can establish gross or willful negligence on the part of the contractors, it may be able to void such indemnities but this is seen as hard to achieve.

I don't think it's built into peoples' expectations, said the second analyst, who also declined to be named due to the legal sensitivities.

BP was widely criticized for trying to shift blame onto Transocean during the crisis. President Barack Obama called the mudslinging among the companies a ridiculous spectacle.

Joseph Lampel, professor of strategy at Cass Business School said a lawsuit would be even more damaging to all the companies.

The lawyers may have a go at each other. They will cross-examine witnesses and they will dig into every detail imaginable. This kind of battle is not only fought in the courtroom but in the arena of public opinion, he said.

What we know about any corporate battle in court, is that it's rare for any side to come out better.

(Additional reporting by Sakthi Prasad in Bangalore and Matt Daily in New York; Editing by Mike Nesbit and Maureen Bavdek)

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