A 90-year-old maritime law gets BP off the hook for workers killed on the Deepwater rig.

That’s because the Deepwater rig is legally considered an oceangoing vessel and was more three nautical miles offshore at the time of the accident. As a result, the families of the dead workers can only sue BP and its contractors under a 90-year-old maritime law, the Death on the High Seas Act, which severely limits liability. In some cases, BP could get away with shelling out sums as paltry as $1,000.

Gordon Jones, a mud engineer killed on the Deepwater rig, left behind a pregnant wife who had quit her job to stay home with their 2-year-old son. But thanks to DOHSA, the most BP could owe them is the equivalent of Gordon’s salary over his working life, minus what he would have paid out in taxes and personal expenses. So if Gordon made $60,000 a year for the next 30 years, BP could owe the family less than a million dollars.

The math works out even worse for workers without dependents. Jones’ brother Chris testified before the Senate Judiciary Committee that one of the other Deepwater workers who was killed was single and childless. That means his family would only be entitled to recover funeral expenses under DOHSA. But because his body was never recovered after the explosion, the funeral costs will be lower. BP could end up paying his family as little as $1,000 for their loss.