about oil spills from the "exxon valdez" or about the recent spill in the gulf of mexico that british petrolm in illing provoked. you're talking about a whole different set of problems. how do they compare with those big spills? micah: it's a great question. i think we all get our attention awn to the big dramatic moment. explosion of an oil rig, the sinking of a giant oil tanker. but in fact, over time, if you look at the total cumulative effect of that, it's only about 20% of the oil that goes into the ocean from human sources. the much larger component is this relar, everyday, intentional dumping overboard, getting rid of oil, waste products, sludge. ships--commercial ships tend to burn very low-grade oil, and that produces this messy sludge. and the question is, what do you do with that? well, by law, you're supposed to bring it to port, you're supposed to offload it. it takes time, it takes money, it takes energy to properly dispose of this stuff. or, if you're not trying to obey the law,ou can just dump it overboard, which the shippers believe save them time and money. mariners traditio