An oily sheen has spread around a stricken North Sea gas rig, Greenpeace activists on a ship nearby said Monday, but Total insisted it was formed by gas condensate.Greenpeace's Koenigin Juliana research ship arrived on Monday at the edge of an exclusion zone around the abandoned Elgin platform owned by Total, 150 miles (240 kilometres) off Aberdeen in eastern Scotland.
The French energy giant insists there has been little environmental impact since the gas began leaking from the platform on March 25.
But Christian Bussau, a marine expert from Greenpeace who is on board the ship, said a multi-coloured sheen around the platform was spreading and the group was taking air and water samples.
He said he believed the substance to be oil, though he admitted Greenpeace would not be able to analyse its samples until the ship returned to its base in Germany.
"This is a really big accident," Bussau said from the Koenigin Juliana, which is about three nautical miles from the platform. "Total must immediately start to close the leak, or the pollution won't stop."
Total has readied a Hercules military transport plane carrying dispersant that could be sprayed on the sheen, but said it did not expect it would be necessary to deploy it.
It says the sheen is caused by gas condensate, or gas that has turned to vapour.
"The light condensate poses no significant threat to seabirds or other wildlife," a Total spokeswoman told AFP.
Greenpeace dispatched the Koenigin Juliana from Germany on Saturday.
"Oil companies often withhold information when there are accidents," Bussau said. "We want to get our own picture of the environmental damage from the scene."
Total, which has seen an estimated eight billion euros ($10 billion) wiped off its stock value since the leak was discovered, is awaiting British regulators' advice on whether it is safe to approach the rig.
The Health and Safety Executive (HSE) told AFP its officials would meet with Total in Aberdeen on Monday, while the energy giant said it was assembling a crew to go on to the platform "in the next couple of days".
Total said the crew would include outside experts from Texas-based firm Wild Well Control. They were among the experts who worked to stem the massive oil spill following an explosion at BP's Deepwater Horizon rig in the Gulf of Mexico in 2010.
Total is preparing to drill two relief wells to stop the gas leak, in parallel with an operation to pump so-called "heavy mud" at high pressure into the stricken well.
The last of Elgin's 238 crew were evacuated on March 25, while Total's Anglo-Dutch rival Shell has also been forced to halt output at its Shearwater platform and Noble Hans Deul rig, four miles away, because of safety concerns.
The last major accident in the North Sea was in 1988, when the Piper Alpha oil platform operated by the US-based Occidental Petroleum exploded, killing 167 people.
Total's British rival BP is still recovering from damage to its reputation and finances caused by the Deepwater Horizon spill.