Deepwater Horizon Oil Spill

Track the size and extent of the 2010 Deepwater Horizon Oil Spill

NASA Earth Observatory image modified by SkyTruth

Deepwater Horizon Oil Spill

Deepwater Horizon Oil Spill

Track the size and extent of the 2010 Deepwater Horizon Oil Spill

NASA Earth Observatory image modified by SkyTruth

Step 1: Learn about the Deepwater Horizon oil spill

Track the size and extent of the 2010 Deepwater Horizon Oil Spill


In April 2010, the largest accidental oil spill in the world’s history occurred in the Gulf of Mexico when BP’s Deepwater Horizon oil well exploded.  For months scientists tried to contain the spill to protect fish, wildlife and communities along the Gulf shore.  No one was sure how much oil was spilling into the Gulf during this time or how to fix the well to stop oil from fouling Gulf waters.  But a small non-profit organization called SkyTruth used satellite imagery to estimate the size of the spill.  News media reported these results to the public and government officials, and eventually government scientists calculated the true size of the spill. In July 2010, almost 3 months after the oil well exploded, BP managed to cap the well and stop the spill.

In this activity you will look at the same satellite images used by SkyTruth to track the oil spill, measure its growth over time, and calculate the volume of oil leaking into the Gulf.  You will also read newspaper articles documenting how SkyTruth and university scientists made a difference, and explore how satellite information and input from citizen scientists can help address environmental disasters.

The disaster

Platform supply vessels battle the blazing remnants of the off shore oil rig Deepwater Horizon. A Coast Guard MH-65C dolphin rescue helicopter and crew document the fire aboard the mobile offshore drilling unit Deepwater Horizon, while searching for survivors. Multiple Coast Guard helicopters, planes and cutters responded to rescue the Deepwater Horizon’s 126 person crew. Photo courtesy of the US Coast Guard.

At 10 pm on April 20, 2010, BP’s Deepwater Horizon oil drill rig, 41 miles off the coast of Louisiana in the Gulf of Mexico, exploded. Flames from the 14 story high rig leapt even higher into the air and the onboard crew headed for lifeboats or dove into the water for safety. Eleven of those crew members didn’t make it. They perished as the enormous rig burned. It took almost two days to extinguish the flames and by then, the drill rig had begun to drift and sink.

Soon, another tragedy emerged: crude oil was gushing into the surrounding Gulf from the now “blown out” wellhead submerged under 5000 feet of water. Technologies in place at the wellhead to prevent oil from pouring into the water in case of emergency weren’t working. Engineers were going to have to find new solutions.

To learn more about how safety measures at the wellhead failed, view the multimedia presentation “Investigating the Cause of the Deepwater Horizon Blowout” by the New York Times.

The problems now became twofold: fixing the wellhead to stop the flow of oil and protecting the Gulf of Mexico’s vulnerable fish, wildlife, and coastal communities from the rapidly spreading oil.  As engineers struggled to develop and install technologies to cap the well over coming weeks, oil continued to spill into the Gulf.  Cleanup crews tried to contain the oil at the water’s surface with absorbent booms to keep it from flowing onshore into coastal wetlands that nurtured young fish, shellfish and shorebirds. Airplanes dropped chemicals that dispersed the oil into tiny droplets, hoping that doing so would reduce the oil’s toxic impact. But the oil continued to spread.

To see where and when oil reached the coast, view the interactive presentation “How much oil is on the Gulf Coast” by the New York Times.

Understanding the problem

The spill continued for almost three months until it was finally contained.  Over that time, oil on the water’s surface had spread far from the original wellhead across an area the size of the state of Oklahoma.

SkyTruth cumulative BP spill as of July 16, 2010.

The above image is a map showing cumulative oil slick footprint from BP / Deepwater Horizon oil spill, based on satellite images taken between April 25 and July 16, 2010, created by SkyTruth.

While it was happening, no one knew how long it would take to stop the spill, how deeply the spreading oil reached below the surface, and how much oil was actually spilling.

See a visual presentation by the New York Times about the spread of oil.

[A link to the Times-Picayune presentation at has been removed because it used Adobe Flash, which is no longer supported.]

Early on in the spill, the US Coast Guard – the federal agency in charge of working with BP to clean up the spill – estimated that 1,000 barrels of oil (42,000 gallons) were leaking from the blown out well each day.

In those first few weeks, journalists informing the public of the dangers and the causes of the spill relied on announcements from the Coast Guard and BP in their news stories. But no one knew for sure whether the levels were true, just how much cleanup would be required, or what lessons oil companies, the government, and the public should learn about the dangers posed by drilling in deep waters of the Gulf of Mexico.

Satellite imagery provides some answers

A thousand miles away an environmental group, SkyTruth, was watching the events unfold. SkyTruth uses satellite imagery to study and document environmental impacts on earth. Oil spreading across the sea surface leaves a sheen that changes the surface of the water, making it look different from surrounding water. This difference often can be detected in the images taken by satellites circling the earth. SkyTruth alerted scientists at Florida State University and the University of Miami about the possibility of a major spill.  It began gathering satellite images from NASA’s MODIS website (which stands for Moderate Resolution Imaging Spectroradiometer) and other images made available through the University of Miami.   It then used the images it collected to examine how far oil had traveled on the water’s surface, and estimate how much was actually leaking into the Gulf.

Step 2: Calculate the size of the oil spill

How big was the spill?

SkyTruth obtained satellite images from NASA and the University of Miami every few days for weeks following the spill to track the oil’s spread. Using the same images that SkyTruth used, calculate the size of the BP oil spill on three different days early in the spill as it continued to spread.

Area: how big was the spill?


1.  First, go to the Guide to Using Google Earth and download the instructions on how to use Google Earth to document the oil spill on satellite images.

2.  Then, go to the satellite images of the oil spill provided in the KMZ file.  Practice using Google Earth on the image provided of April 25, 2010 and record your result in the calculations worksheet provided.

3.  Pick either April 27 or April 29 to determine your second area.  SkyTruth identified the slick area on April 27,  but clouds on that day can make identifying the oil slick confusing.  See if you can outline the oil slick despite the clouds on April 27, as SkyTruth did.  Or, outline the slick two days later on April 29, when clouds didn’t disrupt the view.

4.  Finally, outline the spill area on May 1.

Volume: how much oil was this?

The area affected by the spill measures only one dimension of how much oil entered the Gulf — the size of the sheen that could be seen on the top of the water. The other dimension is how deep that oil is below the surface. Oil only 1 micron (µm) thick (that’s 0.000001 meters — less than 1/3,000th the thickness of a human hair) can leave a surface sheen that is visible by satellites. In many cases, the oil is much thicker than that, but scientists don’t  know just how thick.

To estimate the minimum amount of oil entering the Gulf, SkyTruth used the thinnest amount of oil it would take to change the surface characteristics of the water and be detected by satellite images, or 1 µm. It then multiplied that amount by the area of the spill to calculate the volume.

Exercise: use the calculations worksheet to calculate the  volume of oil in the oil spill for each date using the formulas provided.

To calculate its minimum estimate, SkyTruth assumed the oil was the thinnest possible and still be detected by satellite images. But on April 27, one week after the spill, a BP executive stated that 3% of the spill area was actually 100 µm thick. If 3% of the spill area on April 27 was 100 µm thick and 97% was at least 1 µm thick, how much oil had spilled into the Gulf of Mexico in the first week?

Rate: how much oil was flowing into the Gulf each day?

Rate = total volume of oil leaked/ # of days leaking

Exercise: calculate the oil flow rate April 27 or April 29, about a week after the explosion.

Compare your results with SkyTruth’s

April 25 =   2,103 km2

SkyTruth didn’t calculate a volume or flow rate for this date.  If their area calculation is different from yours, calculate for them what the volume and flow rate was on this day, based on their interpretation of the images.

April 27

Area = 5,783  km2

Volume = at 1 µm thick = 5,783 cubic meters (m3) of oil or 36,374 barrels

Rate =36,374 barrels/7 days = 5,196 barrels/day

SkyTruth concluded that, at a minimum, more than 5,000 barrels were spilling to the Gulf each day by April 27.  They didn’t calculate on April 29.  If you calculated the size of the spill on April 29, how much larger did it get in just 2 days?

But if 3% of the area was 100 µm thick, as the BP executive said, and the remainder (5,609.5 km2) was 1 µm thick then the volume is: 22,960 m3 of oil;  144,414 barrels.

May 1:  6,734 km2

Combining satellite imagery with aerial overflights by the Coast Guard, SkyTruth estimated a flow rate of 26,500 barrels/day.

Step 3: Determine the impact of your spill estimates

The impact of imagery

In the first few days after the explosion, the Coast Guard and BP told the public that only 1,000 barrels of oil per day were leaking out of the blown out wellhead. As SkyTruth began publishing its higher estimates of the spill on its blog and social media, reporters began to notice. On April 27 SkyTruth and Dr. Ian MacDonald of Florida State University estimated a flow rate of at least 5000 barrels based on the minimum thickness of oil at the surface needed to be detected by satellite imagery. They estimated a more likely flow rate of at least 20,000 barrels per day if the oil was thicker than that.  One day later, the National Oceanic and Atmospheric Administration (NOAA), responsible for fisheries and other marine life in federal waters, announced their estimate of 5,000 barrels per day. That estimate remained the official government estimate for weeks.

The Guardian Article “Gulf oil spill ‘five times’ larger than estimated“,  April 29, 2010

But on May 1, SkyTruth and Dr. MacDonald released a new estimate showing an even higher flow rate based on maps created by the Coast Guard after flying airplanes over the spill area. That new flow rate was over 26,500 barrels per day. Yet federal agencies and BP continued to insist that the spill rate was only 5,000 barrels per day.

Once SkyTruth revealed its estimates of the spill, news organizations reported it.

Los Angeles Times article “Oil spill five times as large as earlier thought“, April 29, 2010

Newspapers across the country revealed the discrepancy between what BP and the Coast Guard were claiming and the images analyzed by sky truth. Television and online news programs such as NBC, CNBC and others featured SkyTruth in their newscasts.

Soon thereafter, on May 19, the federal government convened a panel of scientists, called the Flow Rate Technical Group, to calculate an official flow rate. A week later, the group of scientists estimated a minimum flow rate of 12,000 to 19,000 barrels per day.

New York Times article “Estimates Suggest Spill Is Biggest in U.S. History“, May 28, 2010

As they continued to gather new information – including video footage of the seafloor well, pressure readings from the wellhead, and computer simulations — the scientists revised their estimate upward.

Washington Post article “Scientists offer varied estimates, all high, on size of BP oil leak“, June 11, 2010

Months later, they indicated that the flow rate was 53,000 barrels per day – 53 times higher than the original Coast Guard and BP estimate.

If you want to learn more about the combination of scientific approaches the federal Flow Rate Technical Committee used to calculate a more accurate flow rate, review their final results.

The emergency ends, but its effects linger

On July 15, 2010, (after 87 days) BP engineers finally found a way to cap the well and stop the spill. Oil stopped gushing into the Gulf of Mexico, but oil already leaked lingered for weeks.  Although most of the visible oil eventually disappeared, the long-term impacts on marine life – including oysters, fish, dolphins, seabirds and more — remain unclear. Scientists continue to study how much oil remains in the Gulf and its impact on marine life.

If you want to learn more about the long-term biological impacts of the spill, compare and contrast recent reports released by the National Wildlife Federation and BP.  How do different points of view  influence the interpretation of scientific results?

Ultimately, federal scientists estimated that more than 4 million barrels of oil spilled into the Gulf of Mexico over the 3 month period, making the Deepwater Horizon disaster the largest oil spill in history.

See an interactive map of how much oil spilled at “Tracking the Oil Spill in the Gulf” by the New York Times.

In January 2015, after years of scientific and legal analysis, the U.S. District Court in New Orleans determined that BP was responsible for 3.19 million barrels of oil spilled into the Gulf of Mexico from the Deepwater Horizon. BP had argued that it was only responsible for 2.45 million barrels of oil, considering the oil that it had removed during cleanup efforts. The federal government argued that BP should be responsible for 4.19 million barrels of oil. Under the Clean Water Act, BP could owe the American public $13.7 billion in penalties for damaging public resources with its Deepwater Horizon disaster – $1,000 to $4,300 for every barrel of oil spilled.  The amount it will pay will be determined in a future court case.

New York Times article “Judges Ruling on Gulf Oil Spill Lowers Ceiling on the Fine BP is Facing“, January 15, 2015.

For an independent perspective on the spill’s impact, read or listen to NPR’s analysis on the spill’s five-year anniversary, “5 Years After BP Oil Spill, Effects Linger And Recovery Is Slow“.

Discussion questions

  • What was the difference between Sky Truth’s estimates of the spill and the Coast Guard’s announcements of the spill size? Why do you think these were different?
  • Why do you think the government began revising its estimates? What role did satellite imagery, SkyTruth, and university scientists play in identifying a more accurate flow rate?
  • Why does the amount of oil spilled matter?
  • What roles do different entities play in resolving an environmental disaster such as this? What role does government play? What role do businesses play? What role do university scientists play? What role do private citizens and nonprofit organizations play? What role does the media play?
  • How can information like this be used to avoid or minimize oil spills in the future?


To complete this exercise, students will need:

For teachers, there is a guide for teachers and a teacher version of the Deepwater Horizon Oil Spill KMZ file, in addition to the above resources.

Background Reading:

Extended Learning:

The satellite images capture only the amount of oil at the surface. The amount of oil beneath the surface remains unknown. The National Oceanic and Atmospheric Administration has developed a simple demonstration to help students understand this concept. You can find it at: