Ed Overton, Professor Emeritus of Environmental Science at Louisiana State University, will appear on the Monday, May 24 episode of Late Show with David Letterman to discuss the Gulf oil spill. Ed Overton, professor emeritus of environmental science at Louisiana State University, will appear on the Monday, May 24 episode of The Late Show with David Letterman to discuss the Gulf oil spill. Overton has been a go-to source for national media on the Gulf oil spill disaster, interviewed by NBC Nightly News, the New York Times and the BBC, among others. The professor also has been leading a team of researchers, contracted by the National Oceanic and Atmospheric Administration's Response and Restoration Division, in testing dispersants and oil composition. The information allows them to then determine whether oil and tar samples from different areas trace back to the BP spill.