The spill occurred yesterday, on April 19, following a road traffic collision. But a cleanup operation is still underway for the second day today, on April 20, causing continued delays for drivers.
Oil was spilt after a lorry collided with the central reservation.
National Highways reported this morning the cleanup was still taking place and would likely last through the morning.
It said: “The M25 clockwise in Hertfordshire remains closed between J23 and J25.
“The road is likely to remain closed throughout the morning due to the complex nature of the clean-up.
“There are delays of 90 minutes between J21 and J23.”
The agency asked drivers to consider alternative routes to lessen delays.
The Metropolitan Police issued similar advice, telling divers to “avoid the area”.
A spokesperson for the service, quoted in HertsLive, previously said: “Police are at the scene dealing with a lorry that was in a collision on the M25.
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All four lates between junctions 11 and 10 while emergency services attended the scene.
Two remained closed for some time afterwards, causing delays to continue.
Reports suggested even as the lanes reopened traffic was moving at only around 10 miles per hour back to Junction 14.
On the other delayed stretch of the M25, HCC Highways confirmed at just past 9am this morning queues were continuing for a second day.
It said in a post on Twitter: “Severe delays throughout the Hertfordshire Network this morning due to the M25 closure between J23 and J25.
“Expect long delays if driving in this area.”
Photo footage from motorway cameras show a vast number of cars and lorries queuing on the M25 and it is expected more time is needed for traffic to return to normal.