Within a week of the ExxonMobil tar sands oil pipeline burst in Mayflower, Arkansas, ExxonMobil was in charge of the clean-up, the U.S. government had established a no-fly zone over the area, some 40 residents were starting their second week of evacuation, ExxonMobil was threatening to arrest reporters trying to cover the spill, and several homeowners had filed a class action lawsuit seeking damages from the world's second-most-profitable corporation, which had helped keep the pipeline secret from terrorists.

Before March 29, even some people living next to ExxonMobil's Pegasus pipelinedidn't know it was there. All that changed abruptly around 2:45 pm that Good Friday afternoon, when a resident of the suburban subdivision reported a fresh rivulet of diluted Wabasca heavy crude oil from Canada snaking across the lawn, pooling around children's yard toys, filling gutters, and flowing on down the street, to the nearest storm drain.

(Horrendous slideshow here)

And it smelled! The smell carried for miles. Up close, prolonged exposure was potentially unhealthy, for lung, brain, peace of mind. Environmental responders monitored the air quality for days, but only some of the cleanup workers wore breathing masks.

The pipeline gushed for almost an hour before ExxonMobil had it shut down.

The cleanup began at once and continues. Local volunteers responded immediately to keep the spill from entering nearby Lake Conway, with apparent success so far. Rain hasn't helped. ExxonMobil has promised to be there till it's done. Local, state, and federal teams are also on site, but the situation remains fluid, as it were, with potential impacts possible from local to global.

Eight days into the Mayflower spill, here are some of the questions it raises and some of the current answers, subject to future refinement.

1. Why Didn't People Know They Were Living Near a Pipeline?

Excellent question. And if it gets to court as a real estate dispute, a judge may have to weigh the comparative negligence of a seller's failure to disclose against a buyer's failure to do due diligence.

But government decisions in recent years made due diligence more difficult. After September 11, 2001, fear of further terrorist attacks led to concern about the pipeline as a target. As the local KTHV television station reported, "details of its location were somewhat suppressed, but the information has become more public since then."

2. Is That Why There's a No-Fly Zone, Fear of Terrorists?

Probably not. The official Federal Aviation Administration (FAA) notice was effective shortly after 2 p.m. on April Fools Day and stated: "No pilots may operate an aircraft in the areas covered" by the notice, which cited unnamed "hazards" and was effective "until further notice." The area covered is a circle with a 5-mile radius around the spill, up to an altitude of 1,000 feet.

The Arkansas Democrat-Gazette reported on April 3 that relief aircraft in the no-fly zone would be "under the direction of Tom Suhrhoff," who turns out to be an ExxonMobil employee.

The same day, FAA spokesman Lynn Lunsford told Dow Jones that at least one helicopter was needed to move workers around and scout the area for further spills, and that helicopter (or helicopters) needed to be able to move about freely without needing to worry about other aircraft in the area.

A five-minute aerial video, shot by Adam Randall the same day the FAA put the no-fly zone order in place, shows some of the cleanup activities at the subdivision and in the surrounding wetlands, where the oil spread is measured in miles:

Rivulets of oil filled up ravines and trenches in the marshes near Mayflower. Black balls of crude rolled on top of the water, with the major portions of Lake Conway protected by floating partitions.

3. How Big Was the Spill in Mayflower, Arkansas?

Probably nobody knows yet. ExxonMobil said it was providing equipment and manpower sufficient to deal with a spill of 10,000 barrels. ExxonMobil also said that was a "conservative" response to the spill, which they expect is smaller. ExxonMobil considers this a small spill.

Published estimates of the size of the spill range from 2,000 to 12,000 barrels. By April 5, USA Today was reporting the spill as "tens of thousands of barrels of heavy crude oil."

The U.S. Dept. of Transportation's Pipeline and Hazardous Materials Safety Administration estimate is 3,500-5000 barrels. (A rough estimate based on the pipeline capacity of 90,000 barrels per day, with the pipeline gushing for an hour would produce a spill of about 3,750 barrels of Wabasca heavy crude tar sands oil.)

By the standards of the Environmental Protection Agency (EPA), a "major spill" is anything more than 249 barrels.

Regulators recently levied a fine of $1.7 million on ExxonMobil for a July 2011 spill in the Yellowstone River in Montana, where the amount of oil spilled was about 1,500 barrels.

4. What's the Worst That Can Happen from This Spill?

The biggest concern when the spill was first discovered was that the raw oil would reach Lake Conway, only a mile from the hole in the pipeline.

As an Arkansas state promotional website explains:

At 6,700-acres, Lake Conway is the largest man-made game and fish commission lake in the United States. Construction of the lake began in 1948, with its waters coming from the runoff of Stone Dam Creek, Gold Creek, Palarm Creek, Little Cypress Creek and Panther Creek. Its average depth is six feet, with a maximum depth of 18 feet. The lake is approximately eight miles long with 52 miles of shoreline.

The lake is separated from the pipeline by an Interstate highway (a source of daily pollution itself), and within a few days of the spill the oil had migrated under the highway past several sets of oil booms set out by ExxonMobil.

So far the spill has injured or killed 16 ducks, two turtles, and a muskrat.

5. Who Filed a Lawsuit? And on What Grounds?

Two residents of the polluted Northwoods subdivision, Kimla Greene and Kathryn Jane Roachell Chunn, filed a class action lawsuit in federal court in Little Rock on April 5, seeking an unstated amount of damages on behalf of themselves and their neighbors, anyone living within 3,000 feet of the burst pipeline.

The suit seeks compensation for damage caused by the pipeline failure, including lost property values, environmental damage, and other harm, the value of which could reach several million dollars, if they win the case.

6. Who Decided Who Should Be Evacuated?

The Mayflower Incident Unified Command includes ExxonMobil, Faulkner County, the EPA, and the City of Mayflower. Local officials reportedly recommended the evacuation of 22 houses closest to the pipeline soon after the spill occurred. There seems to have been no resistance. ExxonMobil has promised to pay the expenses of the some 40 people evacuated. The City of Mayflower maintains a web site with details of the spill and response.

Residents may not be allowed to return to their homes for a month or more. So far they have filed about 140 claims with ExxonMobil.

7. Who Instituted What Amounts to Martial Law in the Subdivision?

Nobody, at least not officially. Some reporters have complained about the heavy-handed controls imposed by authorities, who have effectively closed off the spill zone as they see fit. Suzi Parker in Grist argued that ExxonMobil "has instituted something like martial law."

Lisa Song from Inside Climate News and Michael Hibblen of local public radio KUAR described similar encounters with the Faulkner County Sheriff's Department. Both recount the sheriff's deputies first denying them access to the site and herding them into a restricted area. Then, soon after, without explanation, the deputies ordered the reporters to leave within 10 seconds or face arrest for criminal trespass.

This use of county sheriff departments is a pattern in East Texas, where TransCanada is building the Keystone XL pipeline to carry more dilbit, tar sands oil, to Gulf coast refineries. In Texas the deputies under the control of TransCanada used pepper spray, physical violence, and forms of torture on protestors before arresting most of them. There have been no reported arrests in Arkansas.

8. What's the Difference Between Wabasca Heavy Crude and Tar Sands Oil?

Little or nothing.

If there's any significant difference, it's not widely known yet. It all comes from the same wide region of Canada, it's all bitumen, and it all has to be diluted to be moved by pipeline. What's in the pipeline is all diluted bitumen, or dilbit.

It's hard to find out what the dilutants (or diluents) are, which is probably important.

9. Where Does Wabasca Heavy Crude Oil Come From?

Wabasca Heavy comes from the tar sands region of Alberta, Canada. It moves primarily via Pembina and Rainbow pipelines to Edmonton and on to the pipeline nexus in Hardisty. From there it is distributed to destinations in Canada and the U.S.

One route takes Wabasca Heavy through the existing Keystone pipeline to Patoka, Illinois. There it transfers to ExxonMobil's Pegasus pipeline which takes it to Nederland, Texas, by way of Mayflower, Arkansas, about 25 miles north of Little Rock.

10. What Is this Pegasus Pipeline?

ExxonMobil owns and operates the Pegasus pipeline, a 20-inch diameter pipe that is 858 miles long and is mostly buried between Patoka, Illinois, and Nederland, Texas.

Pegasus was built in the 1940s, to bring refined oil north from Texas. In 2006, ExxonMobil reversed the direction of the pipeline's flow to carry Wabasca Heavy south. In 2009, ExxonMobil increased the carrying capacity of the pipeline by 50%, to 90,000 barrels per day. Published estimates of its carrying capacity range from 80,000 to 95,000 barrels per day.

An ExxonMobil press release announcing the expansion added that: "Operational enhancements, such as new leak detection technology, were also incorporated to support ExxonMobil Pipeline Company's primary focus on operating its pipelines in a safe and environmentally responsible manner."

The federal class action lawsuit alleges that these changes – including reversing the flow and increasing the capacity – weakened the pipeline and contributed directly to its failure in Mayflower.

On April 3, CBS News reported – falsely – that the pipeline had "carried crude oil from Canada to Texas for decades." CBS did not mention tar sands, bitumen, or dilbit, treating the spill by omission as if it were not unusual.

In 2010, ExxonMobil was fined $26,200 by the Pipeline and Hazardous Material Safety Administration for failing to inspect the Pegasus pipeline as frequently as required by law.

The pipeline was last inspected in February 2013, but the results are not public.

11. So What Happens to the Wabasca Heavy in Nederland?

In Nederland, which is part of the greater Beaumont-Port Arthur metropolitan area along the Gulf coast of Texas, Wabasca Heavy will leave the pipeline for processing at one of the many local refineries.

12. Does Diluted Bitumen/Dilbit Corrode Pipelines Faster Than Other Oil?

The answer is in dispute.

Environmental groups like the Natural Resources Defense Council (NRDC) say dilbit corrosion is greater, based in part on the fact that pipelines carrying dilbit oil have spilled 3.6 times more oil than the U.S. average. A study by the Alberta government concluded that dilbit oil causes more pipeline failures than conventional oil. These arguments address somewhat different questions. The U.S. National Academies of Science has a committee studying the question, but it has so far been hampered by the unwillingness of pipeline companies to share sufficient data.

13. Has Dilbit Oil Ever Spilled Before?

Of course, although records are not comprehensive. The most notable diluted bitumen spill in recent history was in 2010, when an Enbridge owned-and-operated pipeline burst and dumped an unknown amount of tar sands oil into the Kalamazoo River in Michigan, polluting some 40 miles of river and wetlands.

The Kalamazoo River cleanup is now in its third year and has cost more than $800 million so far.

14. Who's the World's Most Profitable Corporation?

Gazprom, the Russian oil company, with almost $44.5 billion in annual profit, as reported in Fortune's Global 500 list (using 2011 data).

ExxonMobil is #2, with annual profits of $41 billion. This is good enough to rank ExxonMobil #1 among American corporations, way ahead of #2, Chevron, with annual profits of $26.9 billion.

Coming in third, at $32.2 billion a year, is the Industrial & Commercial Bank of China.