After dealing with one aspect of its troubled past — its tumultuous relationship with Russia — BP (NYSE:BP) seems like it might finally be heading toward closure on another issue: its legal problems.

Ever since the integrated energy major’s 2010 Deepwater Horizon rig disaster in the Gulf of Mexico killed 11 workers and created one of the worst oil spills in recent history, BP has been fighting a tough battle. Poor earnings, legal overhangs, asset sales galore and public backlash have hampered the firm’s prospects in the nearly two years since the spill.

That battle seems close to an end, as BP has agreed to plead guilty to criminal charges from the Justice Department. However, that plea is going cost them — a lot.

A Record Fine

Over a period of 87 days in 2010, BP’s Deepwater Horizon spilled an estimated 200 million gallons of crude into the Gulf of Mexico, causing countless environmental damage to the southern United States. And BP finally is ready to admit wrongdoing on its part.

According to Reuters, the company is expected to plead guilty to criminal misconduct for the disaster and will be expected to pay a record criminal penalty through a plea agreement. That fine is estimated to be between $3 billion and $5 billion, making it the highest corporate criminal settlement assessed by the Department of Justice. (The previous record was a $1.2 billion fine imposed on drugmaker Pfizer (NYSE:PFE) back in 2009.)

The fine also would dwarf BP’s other major settlements with the DoJ. Back in 2007, the oil firm paid about $373 million to resolve three separate probes into a deadly 2005 Texas refinery explosion, an Alaska oil pipeline leak and a fraud charge for conspiring to corner the U.S. propane market.

However, the kicker in the Deepwater Horizon deal is that up to four BP staffers will face manslaughter charges over the deaths of the 11 workers onboard the rig.

BP already has paid at least $8 billion in damages and recently announced that it expects to make the final payment this year, to a $20 billion trust fund, to cover damage from the blowout. The integrated giant also paid out roughly $7.8 billion in civil settlement claims from at least 100,000 plaintiffs in the Gulf region. The company has been selling assets — from refineries to shale fields — to raise the money to pay for the damages. BP has estimated that it will need to spend roughly $38.1 billion to cover its liabilities from the incident.

BP had long claimed it was not negligent in the spill and after its own internal investigations concluded that no single cause was behind the accident, but “multiple companies, work teams and circumstances were involved over time.” This included the owner of the rig, Transocean (NYSE:RIG), and well cementing provider Halliburton (NYSE:HAL). So far, neither of the two oil service stocks has paid any sort of settlement to BP or the Justice Department for their involvement.

However, back in September of 2011, a team of Coast Guard officials and federal regulators concluded BP bears ultimate responsibility for the rig explosion and resulting spill.

Is This Good News for Investors?

The real question for investors in the beleaguered energy firm is whether the settlement can be considered a positive development. Unfortunately, the answer isn’t that clear.

While the plea does move the case toward finally being resolved on the criminal side, the civil resolution still could be troublesome for the firm. The key piece to BP’s case was the issue of negligence. If the DoJ establishes that BP was criminally negligent in performing safety checks — which a guilty plea would do — then things could get far worse. A gross negligence finding could nearly quadruple the civil damages owed by BP under the Clean Water Act to $21 billion (in a straight-line calculation).

Likewise, the deal would not include other claims from individuals under the Clean Water Act, or various individual state claims for economic loss.

All in all, the legal drama could and will continue to drag on for months.

Given that fact — despite its improving performance and the potential criminal resolution — BP still isn’t a buy just yet.

As of this writing, Aaron Levitt did not hold a position in any of the aforementioned securities.