The Transocean rig had been on fire since the explosion, but is now fully submerged with only burning debris left floating on the surface.
The deepwater rig finished installing an 18,000-foot exploratory well when it exploded on Tuesday.
Barbara Shook is the Houston Bureau Chief of the Energy Intelligence Group and an industry analyst. She says usually the only time rigs are lost is from a hurricane.
"The complete destruction and loss of a facility is a very rare — very, very rare occurence. I don't remember the last time that we had one that was a total loss while it was operating."
This particular rig would cost about $700 million to replace. Oil spill teams are responding to the accident, but Shook says a significant spill is unlikely.
"Actually as long as the fire continues to burn we shouldn't have much environmental impact because the fire will consume the hydrocarbons. The photos seem to show a light sheen, but nothing significant."
Once rescue and mitigation efforts are complete, Shook says the sunken rig may become an artificial reef on the ocean floor.
There were 126 people on board the rig when the explosion happened and 115 have been accounted for. Emergency responders have already searched more than 3,000 square miles by air and sea.
NEW ORLEANS — Assist vessels attempt to extinguish flames aboard the mobile offshore drilling unit Deepwater Horizon as Coast Guard assets search for survivors April 21, 2010. Multiple Coast Guard helicopters, planes and cutters are responding to rescue 126 people after the Coast Guard eighth district command center received a report that the Deepwater Horizon had experienced an explosion at approximately 10 p.m. April 20, 2010. U.S. Coast Guard video by Petty Officer 3rd Class Tom Atkeson.
All images courtesy of the Coast Guards.