Part of the M25 was closed for most of Saturday after a fatal crash in which a petrol tanker collided with a lorry and overturned.
The M25 was empty around the crash scene throughout Saturday
Surrey Police said the driver of the Texaco petrol tanker died at the scene of the crash late on Friday night.
The M25 was closed in both directions between junctions 5 and 6 while spilt petrol was cleaned up.
A Surrey police spokeswoman said the clockwise carriageway reopened before midnight on Saturday.
But she said: "The Highways Agency is still assessing road safety issues on the anticlockwise carriageway and when to reopen it will be their decision."
The road was closed due to the risk of explosion after the fuel spillage.
Police had initially hoped to reopen part of the 10-mile stretch of road by 1200 GMT but later said it would be impossible to get the road clear before the evening.
At 1800 GMT officers said the extra fuel which leaked out of the tanker when it was pulled upright meant the road would not reopen for several more hours.
The M26 was also closed, by Kent Police, because its junction with the M25 was shut.
The collision happened at about 2255 GMT on Friday.
Police said the tanker, heading towards Kent, clipped the back of a lorry in front of it, 6km east of junction 6.
Surrey Police said the tanker, carrying 33,000 litres of petrol and diesel, left the motorway on the left hand side of the road and overturned into a field.
The 30-year-old man driving the tanker was pronounced dead at the scene, but nobody else was injured.
A 200m exclusion zone was set up around the crash scene.
A Surrey Police spokeswoman said: "The decision to close the motorway is never taken lightly and on this occasion was made to ensure the safety of other motorists.
"The key consideration here was the spillage and fumes from the tanker, with the risk of explosion."