US President Barack Obama says Americans have made significant progress in cleaning up last year's prolonged oil spill in the Gulf of Mexico, but says the job is not done. Obama made the statement on Wednesday on the occasion of the first anniversary of the worst offshore oil spill on the Deepwater Horizon oil rig that killed 11 people. Obama said he continues to hold the BP oil company and other responsible parties fully accountable for the painful losses they have caused. Communities on the U.S. Gulf Coast are marking the anniversary with gatherings focused on environmental awareness.