NOAA's Response and Restoration Blog

An inside look at the science of cleaning up and fixing the mess of marine pollution

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What’s in the Oil from the Deepwater Horizon Spill? What’s in ANY Oil?

Heavy band of oil in the Gulf of Mexico

Heavy band of oil seen during an overflight in the Gulf of Mexico on May 12,2010. Credit: NOAA.

What is in oil? Well, there are literally thousands of individual compounds in oil. So what was in the oil flowing out of the Macondo well in the Gulf of Mexico last summer?

Researchers from the Woods Hole Oceanographic Institution took samples in order to figure this out and just published some of their findings on the chemical composition of the Deepwater Horizon oil in the Proceedings of the National Academy of Sciences [PDF]. You can read a non-scientist’s summary of these findings at Scientific American.

The Scientific American story points out that crude oil is not a single substance but is a mix of different hydrocarbons and other chemicals and trace metals. But did you know that there are also thousands of different kinds of crude and refined oils?

Oil from the Alaska North Slope is really different than oil from Alaska’s Cook Inlet, not to mention places like Angola, Nigeria, or Venezuela. The chemical components of the oil depend on the geologic formation they are extracted from, and even oil from the same geologic formation can vary over time.

Another way to think about this is to imagine separate regions of the world that make “wine.” There are many types of wine, but a merlot doesn’t taste like a chardonnay because the grapes are a different variety. But even a merlot with grapes grown in California will have a distinct flavor from a merlot grown in France, from a neighboring valley in California, and even from the same vineyard from year to year. Why? Because the ingredients in the soil, the weather conditions, and how the grapes were grown create these differences in the grapes. All of these and other factors come together to give you a different kind of “wine.” It’s a similar concept for oil.

Comparing diesel and bunker fuel oils

Diesel fuel, left, is a much lighter oil than the heavy, slow-moving bunker fuel on the right. Credit: Doug Helton, NOAA.

These differences in the ratios of certain hydrocarbons and other chemicals (the varying “recipes” for oils) make a difference in the extraction and refining process—as well as in spill cleanup. Some crude oils are heavy and viscous (sticky and slow-moving), like roofing tar, while others are light, like diesel fuel. Some oils have a lot of sulfur compounds. These are called sour crudes. Oils without a lot of sulfur are referred to as sweet crudes.

Some oils are so heavy that they sink beneath the water surface when spilled, and some are so light that a large fraction will evaporate. Some will mix with water and form stable emulsions, like an oil-based salad dressing. Some oils are amenable to specific response strategies such as burning or chemical dispersants. Because these variations in oil can make a big difference when oil is spilled, we have computer programmers who created and maintain a database of oils and their properties to help make decisions during spill responses.

Our Automated Data Inquiry for Oil Spills (ADIOS2) model has a database containing more than a thousand crude oils and refined products and provides quick estimates of the expected characteristics and behavior of spilled oil.

The database was compiled from different sources, including Environment Canada, the U.S. Department of Energy, and industry. Take a look for yourself at all of the information about oil in the database, and then create a mock spill to calculate how much of the oil would have evaporated, been naturally dispersed in the water column, and is still remaining on the water surface.