It's hard to imagine a scenario where BP will not be held accountable for a huge chunk of change. Even the oil financed politicians are likely to be gun-shy about fighting a full liability bill. Most are smarter than Barton. (But the Rs should dump him from any energy policy position, which they seem loath to do.)
That said, I do not believe BP will pay for ALL the damage they have done, but I’m equally sure they will pay one hell of a lot more than Exxon ever did. For one they have already coughed up $20 billion.