1. Are these spills very common?

Huge blowouts (explosions, followed by fire, occurring when wells are being drilled), occurring in US waters, are uncommon. The last one was the Santa Barbara Union Oil Blowout in 1969 - a little over 40 years ago. The leak lasted 11 days, and the amount of the spill was estimated to be 200,000 gallons (5,000 barrels of oil), so was less than the amount of the current spill. But it was close to shore, and the oil damaged beaches, besides affecting wildlife.

Much more common are oil spills, typically occurring when a ship powered by oil, or a ship carrying oil, collides with another object. The biggest recent oil spill in US waters was the Exxon Valdez oil spill, which occurred in Alaska in 1989. This occurred when an oil tanker ran aground, and spilled 10.9 million gallons (250,000 barrels of oil). If the current spill is 1,000 barrels a day, the Exxon Valdez spill would be the equivalent of the spill continuing for eight months. No one expects the current spill to continue for that long.

An analysis from NOAA shows that there have been many oil spills from ships over the years. Modern double hull oil tankers are not as susceptible to spills, but the many small ships (especially low budget, unlicensed ships) carrying goods of all types can and do run aground, causing smaller spills. The US Coast Guard has regulations to try to prevent problems of this type.

Besides spills, there are naturally occurring underground seeps that allow hydrocarbons to enter the water. In fact, it is these seeps that led to the discoveries of many of the oil deposits found at sea. National Geographic talks about huge underwater asphalt volcanos being discovered off of California, caused by underwater eruptions of hydrocarbons. These eruptions likely caused huge oil slicks.

2. How did the blowout occur?

The earliest oil wells in the Gulf of Mexico were in shallow waters near the coast. But as these wells have become depleted, it has been necessary to drill in ever-deeper waters. When one drills in deeper water, the challenges are greater--the pressures are greater, the temperature of the oil is higher, and the stresses on the metals involved are greater.

The oil industry is creating ever-more technologically advanced equipment to deal with these issues, but the fact remains that it is virtually impossible to solve every new problem that may arise through computer simulations. If one tweaks one part of the equipment to make it stronger (to deal with the higher pressures, and greater temperature differential between the hot oil and the cold water), it can cause unforeseen problems with another system that interacts with it.

Unfortunately, there is an element of trial and error whenever technology attempts to overcome new hurdles. These issues aren't unique to oil and gas--they are just as much challenges to any new technology, including offshore wind and carbon capture and storage technology. While one would like to move smoothly from one technology to the next, in a short time frame, one really must test equipment in the real world. This means progress tends not to be as fast as one would like: it often is punctuated by setbacks when something that looks like it would work in computer simulations, doesn't really work, or when some unforeseen combination of events takes place.

We don't yet know precisely what happened to cause the blowout--there will no doubt be months of investigations. The basic idea of what happened is that Transocean, under contract with BP, was attempting to drill a new well, not too far from existing wells in a deep water area of the Gulf of Mexico. The well was almost complete--in fact, the well seemed to be far enough along that the danger of blowout appeared to be very low. The casing had been cemented, and work was being done on getting a production pipe installed.

Apparently, a pressure surge occurred that could not be controlled. While the equipment includes all kinds of controls and alarms, and a huge 450 ton device called a blowout preventer, somehow it was still not possible to control the hydrocarbon flow. At such high pressures, some of the natural gas separated from the oil within the hydrocarbon stream and ignited causing the explosion.

Some of our readers have provided their ideas as to what might have happened. Rockman has suggested that the strength of the pipes (to withstand the underwater pressure) might have made it impossible for the shear rams in the blowout preventer to slam shut and cut off the pipe, as they were intended to do. Westexas has suggested that perhaps metallurgical failure at such great depths may have contributed to the accident. It is possible that there was some element of human error as well. Without a thorough investigation, it is impossible to know exactly what happened, and even then, there are likely to be gaps in our knowledge.

3. What is being done to stop the leak?

For the last several days, BP has been trying to use sub-sea robots, operating at 5,000 feet below the surface, to engage the blowout preventer and turn off the flow, which seems to amount to about 1,000 barrels (42,000 gallons) per day. With each day that passes, the chance of this working would seem to go down. If the blow out preventer didn't activate properly originally, and hasn't engaged during past attempts by robots, why would a new attempt work any better?

There are two alternative approaches BP is using to cutting off the flow. One approach is to drill a second well to intercept the first well, and inject a special heavy fluid to cut off the flow. Workers will then permanently seal the first well. This procedure is expected to take several months.

The other approach is designing and fabricating an underwater collection device (dome) that would trap escaping oil near the sea floor and funnel it for collection. According to NOAA, this approach has been used successfully in shallower water but never at this depth (approximately 5,000 feet). NOAA reports construction of such a dome has already begun.

Until one of these plans works, the approach is to try control the oil that rises to the surface. According to one source:

BP is throwing all the resources it has available at the spill, so the cost to the company may be substantial. It has deployed 32 spill response ships and five aircraft to spray up to 100,000 gallons of chemical dispersant on the slick and skim oil from the surface of the water and deploy floating barriers to trap the oil.

Another approach that is being tried is burning the oil trapped on the surface. This approach would seem to work best when seas are calm.

Even with these approaches, there is a significant chance the spill will reach shore, perhaps by this week end. Even if it remains at sea, it can be damaging to marine life.

4. How important are wells such as this one for oil production?

In general, the world is running short of good places to drill for oil. There are a few places where oil still can be extracted inexpensively, but these are becoming fewer and fewer in number. What we seem to have left is expensive hard-to-extract oil, especially in this hemisphere.