The salty ocean itself naturally breaks down the oil, albeit even though this a single source of oil release in large amounts over time. The ocean bottom of the Gulf of Mexico releases 100,000 to 400,000 barrels of oil a year naturally. In this case, you won't have repercussions worldwide in terms of ecological disaster. It'd be much more limited. Just possibly at the local or regional level. Then you have hurricanes that can serve to break up the oil even faster. Now, oil on the beach, in the estuaries, etc is a different matter. Then you have the ocean's circulation to think about, too.