Testifying before a house panel on Thursday, an official with the National Oceanic and Atmospheric Administration gave the following estimate: About three-quarters of the oil that spilled into the Gulf from BP’s ruptured well is still in the environment

Federally-funded scientists predicted a "larger than average" dead zone in the Gulf of Mexico this year, but said it's unclear what the oil spill's effects on the dead zone will be.

Dead zones are underwater areas where oxygen levels are so depleted that they're inhospitable to most marine life.