We asked readers to submit their ideas on how the Gulf of Mexico oil spill should have been stopped.
A selection of the hundreds we received has been assessed by Prof Iraj Ershaghi, director of petroleum engineering at the University of Southern California.
BP's cap on the well is currently, according to the company's estimates, capturing more than half of the oil. But could there be a better way?
"Drill a hole next to the well. Place a low-yield nuclear warhead and detonate it.
"The power will fuse the rock together and the intense pressure from the sea water will keep the rock in place thus sealing the leak." - Michael Murray, Greensboro, North Carolina, US
Prof Ershaghi says: "A nuclear blast would not fuse the pipe under the cooling effect of water but rather would create a crater and would make it impossible to control the flow."
"I think you should create a large fabric tube to help control the amount of oil that gets away from the leak. I think something like parachute cloth might work because that fabric is quite a tight weave - water passes through, but I don't think oil would.
"It might have access panels, especially near the bottom where the actual leaks are occurring, but perhaps that would allow for some kind of pump to pump the oily water that would be held within the tube." - Elaine Seniuk, Enfield, Canada
Prof Ershaghi says: "What forces the oil and water to flow through the fabric is a pressure of close to 7,000 pounds per square inch. We also need to realise the volume being produced (15,000-20,000 barrels per day or 600,000 to 800,000 gallons a day). That means capacity requirements that are impossible to create or install under 5,000 ft of water."
"How about using small polystyrene beads impregnated with iron filings to cling to the oil, then pick up the beads with an electromagnet which could be mounted on any number of platforms such as vehicles or boats.
"Beads get processed to remove the oil, then re-used. Cheap to produce, easy to collect from water, better than trying to scrape oil off difficult surfaces. Beads would be easily deployable by air/sea." - Alwyn Turner, Chapel-en-le-Frith, UK
Prof Ershaghi says: "They use straw to help in collecting oil. Any other type of material attachment could result in making the oil drops heavier. Causing the oil droplets to sink will not solve the spill clean-up as we will be polluting the water below the surface. Please also realise, mass production of any new products on the scale of sinking miles of spilled oil on the surface requires months if not years of planning and manufacturing."
PILE OF ROCKS
"How do we block any hole in the earth? By using the natural resources of the earth itself. I suggest that BP utilise barge after barge of rocks that will sink quickly and directly over the outpouring.
"Enough rocks to create a mini-mountain. Sea bed sand might eventually fill the gaps in the rocks as a kind of cement." - Vernon Turner, St Ives, Cambridgeshire, UK
Prof Ershaghi says: "If BP had cut the riser during the first week and had installed a second blowout preventer, a massively heavy 48ft stack, it would have done the equivalent of what you are suggesting. By dropping large pieces of rock, there is no way they can seal all the holes in between the boulders to stop the flow. Use of soft sand will not work for sealing the holes as the flow of high pressure oil and gas will blow away sediment and rocks."
METAL AND MAGNETS
"Wrap electromagnets at different sections of the pipe and secure. Turn on magnets. Inject small metal material into pipe to be attracted to magnets. As material adheres to inside of pipe, inject slightly larger material. Make sure electromagnets are powerful enough.
"Eventually, the flow will decrease and perhaps stop just like a clogged artery in the human body. Remember, power to the magnets must not stop until the pipe is safely capped." - Anon
Prof Ershaghi says: "BP was trying to inject high pressure mud and could not fight the upward flow of oil and gas. It is hard to inject the materials you are suggesting with fluid unless they are pulverized. If they could have been injected, they would have been subjected to the upward pressure and could not have entered the casing."
SINK A SHIP
"I think that the hole could be plugged to greatly reduce the flow, if not end it, by sinking an old ship over the leak.
"If extra ballast were added to the ship to make it even heavier, it would exert enough pressure to seal the hole." - Howard H Rothman, Bridgeport, Connecticut, US
Prof Ershaghi says: "If we used your idea, the weight of the sunken vessel must be enough to overcome the upward force of the fluid while also a tight seal is required over the casing. A better idea is still, as mentioned above, placing another blowout preventer after cutting the riser."
"What will contain it is simply an enormous funnel in thin mild steel which can be lowered over the whole mess with enough pipe of suitably flexible material and diameter to guide the oil to the surface, where of course it will need a constant supply of tankers to suck/pump it safely aboard.
"Obviously the flow-rate and rate of rise needs to be well estimated to get the diameter of the mile of pipe to the surface." - G Vert Vaughan, Veliko Tarnovo, Bulgaria
Prof Ershaghi says: "What BP has done in terms of connecting the Lower Marine Riser Package (the cap on top of the blowout preventer) to take the oil to the surface is similar to your idea, except, they did not have to make a huge funnel to accommodate 800,000 gallons of oil per day."
"Manufacture a series of 30cm custom plugs, each tapered at the front like a bullet. Each plug must have the same diameter as the inner diameter of the tube (minus 2mm to prevent jamming on the way in). However, along the sides of the plugs, cut 100 small diagonal incisions. Thus the plug will look like it is barbed.
"It will go in easily, but dig itself in when going out, plus the more pressure exerted by the gas, the deeper the plug will dig into the pipe sides. Clearly, the plug must be made of a metal harder than the pipe, or it won't be able to do this. Use a pneumatic or even limited explosive charge to deliver the plugs. I suggest a minimum of two - that's how we seal basement leaks in Canada, after all." - Dave Lundy, Canada
Prof Ershaghi says: "Maintaining the integrity of the casing is extremely critical. Use of any hard materials or force against the casing is counter-productive as bursting of the casing could occur. That would make it impossible to control the flow."
"The most obvious solution to me is to use a bladder that is inserted deep into the pipeline, then pumped up with a high pressure medium. Once the flow has stopped and the feed line removed, the end of the pipe may be sealed by whatever caps are required.
"Alternatively, once the pipe is repaired and if it is to be used again the bladder may be deflated." - Mike Konshak, Louisville, Colorado, US
Prof Ershaghi says: "BP could not have done anything of this sort until they cut the riser. One practical solution similar to yours is the use of industry standard coiled tubing. Yes, they could have done that to pump high pressure fluid to fight the well pressure. But one has to be careful not to burst the casing."
"Being an ex-plumber, the only way to deal with a pressurised leak is to keep the open end and connect a fitting to the pipe, then shut the fitting when the pipe connection is made. Underwater and at 5,000ft, you would need to use a skirt, fixed to an open-ended pipe. The skirt could be split on one side. This could be drawn down over the broken pipe end and fixed to a sound portion of the broken pipe, away from the break.
"This could be fixed in place using traditional mechanical fittings, but it is not taking the strain yet, as the pressurised stream is going up the new open pipe and through the split skirt. Then you can slowly draw the skirt closed, re-strengthening the fixings on the sound part of the broken pipe, thus allowing the skirt to take more strain of the pressurised flow. The skirt can be drawn to a close, as the fixings are made good behind it and the pressurised stream will flow up the new pipe to awaiting vessels." - Paul, Canada
Prof Ershaghi says: "The practical way to use your idea, as discussed above, would have been to actually install another blowout preventer over the existing one after BP managed to cut the riser. They did not do that. Still, if the containment device does not stop the flow, they may have to resort to that option."
"To stop the oil flow in the pipe in the Gulf of Mexico, form a funnel that fits into the open pipe and also grips it below the top outside to keep it stable. Pour lead balls of the right size into the funnel to definitely sink into the oil flow despite its speed. They need to be as small as possible while being big enough to be sure to sink. They must be less than about a third of the width of the opening in the funnel to avoid self-jamming in the funnel or pipe and not so large that venturi forces around the balls (from increased oil flow speeds passing the balls) stop them from sinking.
"Reduce the size of the lead balls as the reduced oil flow speed allows smaller ones to sink. When enough lead balls have been fed in to slow down the oil speed, start putting clay balls into the oil pipe. When enough of them have been fed in, put in more lead balls (or steel balls would do by this stage). These last balls will, under the action of gravity, then deform the clay balls to form a seal in the pipe." - Peter Keogh, Olso, Norway
Prof Ershaghi says: "Your idea falls in the category of the junk shot that BP found was not successful."
CRIMP THE PIPE
"Could the pipe be crimped shut? I have read that 'giant shears' were used to cut the pipe, so why not 'giant pliers'? Since capping and siphoning seem problematic, crimping, even if not complete and permanent, should diminish the flow at least partially and until the relief wells or other means can ameliorate the situation.
"Once crimping was used it would deform the pipe so that capping or siphoning would be almost impossible." - Julian P Crane, Everett, Massachusetts, US
Prof Ershaghi says: "Yes, if the blind ram - a device that forms a seal - had worked on the blowout preventer, that was exactly the way the seal process would have taken place to close the casing."
"Epoxy might be a better top kill method than mud, and in any case a heavier solid is needed - try bismuth and/or iron shot. Delivering the resin and catalyst into the well requires two tubes, though an intermediate pulse of isopropyl alcohol may have a chance or separating the two liquids in a single feed tube, there'd be a risk of simply clogging the feed tube before it reached the well.
"Another alternative plug is a torpedo, wire-guided, with a low speed mode (or restrictor) for manoeuvring into place, and an extended warhead holding just enough charge to split containers of epoxy monomer and catalyst." - Jeremy, New Jersey, US
Prof Ershaghi says: "A torpedo or any warhead entering the casing would have made this a major catastrophe as the loss of casing integrity would have resulted in a crater with continuous and uncontrollable oil flow for the next 30-40 years depending on the amount of oil in the reservoir."
"Use an umbrella plug, which would be deployed into the well to the point where the drill borehole breached the well, effectively capping from the inside.
"You could let the pressure of the well secure the plug or fix it to the seabed." - Shayne Dawe, Plymouth, UK
Prof Ershaghi says: "Umbrella type materials that can collapse to fit the pipe and then expand under pressure cannot withstand 6,000-7,000 pounds per square inch of pressure."
SHALLOW RELIEF WELL
"They should drill another hole into the same well and continue collecting the oil. This would diminish the pressure in the currently leaking system, and make it possible to seal the leak.
"If it is possible to hit the current well by drilling into it at an angle, this 'shallow' drill may be faster and easier to do than going all the depth into the reservoir." - Alex, Boston, Massachusetts, US
Prof Ershaghi says: "At the site there are a lot of vessels, the relief well needs to be away from them. You have to go down and then angle it, when you dig the relief well."
UNSCREW THE FLANGE
"It appears that below the cut that they have made before capping the pipe, there is a section of the pipe that is bolted, which combines the two sections of pipe. Wouldn't it be possible to remove the bolts and attach a new section of pipe, bolting the new piece on incrementally, which would allow some leverage in allowing for a rotation of the new section into place.
"The new section could have a valve that could be closed off once this section is put into place, thereby minimising the pressure that they would face when installing this new section." - John Allison, Doylestown, Pennsylvania, US
Prof Ershaghi says: "Such operations would require a tremendous amount of torque and this is very difficult with robots and underwater."
"To clean up the spill itself they could use a hydrocarbon polymer which attaches itself to oil and produces a sponge-like material which would be easier to clean up, or scoop up.
"They could even dye the polymer so that the resultant material is much more visible and again easier to collect." - Steve, Bermuda
Prof Ershaghi says: "Materials similar to what you are proposing are used, but the sheer magnitude of the amounts needed to treat the volume of oil and the timely spread and collection in a speedy manner is not easily manageable."
FREEZE THE WELL
"I know that a lot of wells in the Gulf of Mexico are difficult to produce because of hydrate (methane ice) formation. The containment dome failed because of this. Has the idea of promoting the formation of hydrates within the wellbore itself, to form an ice plug to stop the flow of hydrocarbons, been considered?
"With a reservoir that does not have free water, and producing at above hydrate curve temperatures, the hydrates will not form until the gas has expanded and cooled the surrounding area (Joule Thompson effect). However, if ice cold, fresh water were pumped into the wellbore, perhaps with some ice crystals or grains of sand, or something to promote the seed required to help the hydrate cage form, that may promote the formation of a hydrate plug within the wellbore itself." - Mike, Stony Plain, Alberta, Canada