It could be days before the true scale of the pollution spill affecting sea birds on the south coast is known, wildlife experts said today.
A change in wind direction could have killed thousands more birds after scores were found washed ashore along England's south coast.
Increasing numbers of birds are washing up on the south coast after being covered in a mysterious substance.
Hundreds of seabirds have died after being covered in a "refined mineral-based oil mixture", with many of them found along the Sussex coast, the Environment Agency has said.
Almost 200 birds - mostly guillemots - are being treated at RSPCA centres along the southern coast after they were washed ashore covered in the white, sticky substance.
There was earlier speculation the mystery substance may have been palm oil, but scientists working to identify it have since reported that it is a refined mineral oil.
Staff took samples from the affected water in an effort to establish the cause of the pollution.
A spokesman for the Environment Agency said: "The results show that it is a refined mineral-based oil mixture, but not from an animal or vegetable-based oil, which rules out palm oil."
RSPCA deputy chief inspector John Pollock, who has been leading the rescue mission in Dorset, earlier described the substance as "white, odourless and globular".
He added: "It is like a silicone sealer. The best way I can think to describe it is 'sticky Vaseline'."
Staff at the RSPCA West Hatch centre near Taunton, Somerset, have been treating the birds using margarine and washing up liquid to clean the substance from their feathers.
Peter Venn, manager at West Hatch, said: "What we are hearing are reports of birds showing up on the Sussex coast, so that may mean that the weather is pushing them more easterly.
"This certainly adds up from the basis that we were getting birds earlier in the week from Cornwall, Devon, then up through Dorset and have had birds from Hampshire today, so everything is certainly not over by any means."
Wildlife experts are no closer this evening to discovering what the mystery substance is that has caused hundreds of sea birds to wash up on the south coast.
Most of the guillemots have been found at Chesil Beach in Dorset. But one bird has been found alive as far as Worthing in West Sussex - another, discovered on the Isle of Wight.
More than 100 of the birds have been taken to an RSPCA centre in Somerset as the Environment Agency investigates where the sticky substance has come from.
Martin Dowse speaks to RSPCA Insp John Pollock, volunteer Martin Usborne and Martin Cade from Portland Bird Observatory.
Hundreds of sea birds are feared dead as many are washed up along the south coast. Covered in oil - there are concerns hundreds more could die over the coming days.
Investigations are continuing into how more than one hunded sea birds came to be covered in a greasy film along the Dorset coast. T
The guillemots were found on Chesil Beach in Weymouth.
They were take to an RSPCA recue centre in Taunton where they are being cared for.
Click on the link to see the pictures of the birds at the centre.
An investigation is continuing into how more than a hundred birds came to be covered in a mysterious sticky substance on a 200-mile stretch of coastline in Dorset.
The Royal Society for the Protection of Birds (RSPB) were called to the south coast yesterday after the troubled guillemots, a member of the auk family, were discovered on Lyme Bay near Weymouth.
Environment Agency staff have taken samples of the affected water in an attempt to discover what the mysterious substance is.
Investigations are continuing into how more than one hunded sea birds came to be covered in a greasy film along the Dorset coast. The guillemots were found on Chesil Beach in Weymouth and taken to a nearby RSPCA centre where they are being cared for.
It's not yet know what the sticky substance is but it's not thought to be fuel.
RSPCA staff attempt to treat some of the 100 birds that have washed up on Dorset's beaches, covered in a sticky, greasy substance.
Some have died but most have been taken an RSPCA Wildlife centre. Many have sore legs and early signs are that they are not responding well. And the number of birds coming in has been increasing in the last few hours.
The Maritime and Coastguard Agency have collected samples of this sticky substance for testing . It's not thought to be fuel. But untill its identified, the RSPCA are advising walkers to take care.
Members of the public are being warned about handling distressed birds on the south coast.
During the past 24 hours, a number of live birds have washed up on beaches covered in an unknown substance.
While the substance is being identified, agencies are urging people to avoid coming into contact with the birds and to keep pets away from the shoreline.
If anyone spots an affected bird or animal, they should report it to the RSPCA on 0300 1234 999.
Video just in of bird rescue off Dorset coast. More than 100 birds have been found covered in a sticky substance.