Complex sentence: The 2010 "Deepwater Horizon" oil spill in the Gulf of Mexico has been described as the worst environmental disaster in the United States, releasing about of crude oil making it the largest accidental marine oil spill in the history of the petroleum industry.
Split into simpler sentences: The 2010 "Deepwater Horizon" oil spill in the Gulf of Mexico has been described as the worst environmental disaster in the United States. It released about of crude oil making it the largest accidental marine oil spill in the history of the petroleum industry.