One critical issue for litigation surrounding the Deepwater Horizon explosion and oil spill is liability and damages for ecological harm caused by the disaster. In the latest issue of , RFF Senior Fellow James W. Boyd outlines current damage assessment practices under various federal statutes and their weaknesses, drawing on the lessons learned from the 1989 Exxon Valdez spill and similar incidents. Where established financial measures exist, such as lost wages or forgone revenue, damages from a spill are relatively easy to calculate. But the services that ecosystems provide don’t come with convenient market prices attached. Reasonable people will surely differ on the value of lost sea-grass beds or bird habitats. The ecological and economic damages caused by the BP Deepwater Horizon spill are likely to be very significant and far-reaching, even if they are difficult to calculate with precision. This leaves us with a knotty question for public policy and the courts: how do we appropriately penalize a polluter when we may never actually know the damages they caused? A meaningful penalty is surely called for. But given current scientific and economic knowledge, the scale of that penalty is more likely to be resolved by politics than by scientists. Read this article our interactive flash reader. Also available for download.