Percent Coverage Chart

Use the chart below to estimate the percent of oil coverage in the area you are observing. It was developed for people assessing the percent oil coverage on oiled shorelines, but is also useful for estimating percent coverage of oil on water.

It's easy to overestimate the percent coverage of oil on water or land. To estimate the coverage of an oil spill on water, first estimate the percentage of clean water, and then subtract that quantity from 100 to obtain the percentage of oil. One way to estimate the percentage of clean water is to first imagine that you have collected all the oil together in one corner of the area you are observing, and then estimate the percentage of clean water that would remain in the area.