Journey to centre of oil spill operation
The BBC's science and environment correspondent, David Shukman, gets a bird's eye view of the vast oil spill off the US coastline and learns what is at stake in efforts to cap the leak.
It is only an hour's flight from an airbase in Louisiana to the centre of the oil crisis. But it is a grim journey to another world.
We travel by oil industry helicopter, an aircraft that usually ferries rig workers out to the platforms in the Gulf of Mexico.
But in these days of emergency, it is carrying journalists to witness what is being called one of the worst environmental disasters in modern US history.
From the scorching concrete of an airfield near Houma, Louisiana, we fly south-east over the mangroves and swamps close to the shore.
At first sight from the air, cameraman Ron Skeans and I wonder what the fuss is all about.
But then we see the delicate strips of white stretching parallel to the beaches and reed-beds. They are the booms, trying to keep the oil away from the coastline.
Clusters of boats operate in the channels, sweeping for oil and laying more boom, and a helicopter drops massive sandbags to close the gaps between a chain of islets.
Soon we reach the beach of Grand Isle, a community so badly hit that President Obama has visited it twice.
The sands have been cleaned but only last week I saw fresh oil washing ashore - and from 500ft up, the surf-line still looks stained.
Smell of petrol
The helicopter then turns out over the ocean and the scale of the problem becomes clear.
The oil lies in vast patches on the waves - it is impossible to miss but easy to confuse. Usually it is dark but sometimes has a bright sheen. And occasionally there are lumps of orange-brown.
A US Coast Guard information sheet explains the distinctions between grey sheen (silvery), rainbow sheen (colourful) and metallic sheen (reflecting the colour of the sky).
"The oil will intensify the closer we get to the spill site," crew chief Randy Pearman says. "It will get thicker - and you'll smell it."
He is right. About a mile from the ground zero of this crisis, a faint smell of petrol wafts into the cabin.
And then we arrive - 50 miles from the coast - and the sight is stunning. The gathering of some 20 vessels and rigs must be one of the greatest concentrations of oil industry muscle in one spot.
At the heart of the huddle is the giant tower of the Discoverer Enterprise, the ship now drawing oil up through the "top cap" over the leak.
Blazing from its side is a huge burst of flame - a gas flare. Methane rises with the oil and the fact that is being burned off is proof that the operation is working.
Close by is the ship controlling the robots on the sea-bed.
And also positioned in the inner circle are the two rigs - Development Drillers Two and Three - that all long-term hopes depend on.
These are the rigs drilling below the sea-bed to try to intercept the leaking well and shut it off - the final and best hope of sealing the leak.
Pilot Jim Borger has flown for the oil industry for decades.
"We used to have a blowout about once a year in the Gulf but it was shallower and the oil burned so you had very little pollution," he said.
"This is the first time we've had anything like this anywhere in the world - in such deep water, everything is new."
I ask him how much is at stake.
"The whole offshore drilling industry here in the US - not just in the Gulf but off the east and west coasts as well.
"Everything hinges on what happens right here."