A timeline of the Gulf oil spill.

April 20, 2010: The U.S. Coast Guard receives a report around 10 p.m. of an explosion and fire aboard the Deepwater Horizon oil rig, approximately 42 miles southeast of Venice, La., in the Gulf of Mexico.

April 21: Coast Guard helicopters, planes and cutters respond to the fire. More than 100 people are evacuated from the rig. Eleven crewmembers remain missing.

April 22: BP activates an oil spill response flotilla containing vessels equipped with skimmers, booms and dispersants.

April 23: The U.S. Coast Guard suspends its search for 11 crewmembers missing after the Deepwater explosion.

April 28: An initial controlled burn is conducted to rid oil from the open water. These controlled burns have continued throughout the response.

April 30: The International Bird Rescue Research Center is activated and sends its first team to the Gulf. It reports the same day the finding of its first oiled bird, a northern gannet.

May 2:

- President Barack Obama visits the Gulf Coast, calling the oil leak in the Gulf of Mexico “a massive and potentially unprecedented environmental disaster.”

- Crews continue to test a new technique to break up the oil before it reaches the surface - a remotely operated underwater vehicle that dispenses subsurface dispersant.

- BP begins drilling relief wells.

May 5: First report of oil on the shoreline. Oil is found on the beach at Chandeleur Islands, a small group of uninhabited barrier islands northeast of the Mississippi Delta.

May 28: President Obama makes second trip to Gulf Coast.

May 29: A “top-kill” procedure intended to stem the flow of oil and gas and ultimately kill the well fails.

June 2: The area closed to fishing represents 88,502 square miles, which is approximately 37 percent of Gulf of Mexico federal waters.

June 4:

- President Obama makes his third visit to the region.

- BP lowers a containment device over the source of the BP oil leak, which captures some of the leaking oil.

June 14: Obama makes a fourth trip to the Gulf.

June 15: A small fire is extinguished on the Discoverer Enterprise, a ship gathering oil from the leaking well.

June 16: BP agrees to set up a $20 billion fund for damage claims from the spill. The company also suspends dividend payments to shareholders and says it will pay $100 million to workers idled by the moratorium on deep-sea drilling.

June 17: BP Chief Executive Tony Hayward appears before a congressional hearing.

July 5: Tar balls are spotted just off the Texas coast. Texas is the final Gulf state to be affected by the oil.

July 10: BP begins a "capping stack" procedure, which aims to better stop oil leaking from the well.

July 13: The Obama administration sends a fourth bill, for $99.7 million, to BP and other responsible parties for response and recovery operations. BP and others have paid the first three bills, totaling $122.3 million, in full.

July 15: BP says it has stopped the leak with the new tight-sealing “capping stack” containment cap.

July 22: NOAA reopens 26,388 square miles of Gulf waters to commercial and recreational fishing.

Sept. 19: The well is officially sealed.

Sources: www.deepwaterhorizonresponse.com, www.noaa.gov, www.whitehouse.gov