Passengers faced long delays and diverted flights after the runway at Gatwick was closed because of a spillage.
No flights were able to land or take off at the West Sussex airport after a plane was believed to have dropped oil on Monday morning.
At least 18 incoming flights were diverted to other airports, while outgoing flights were being delayed by up to an hour.
An airport spokesman said several incoming flights were forced to remain in the air and the "priority" was to allow them to land as soon as safety checks had taken place on the runway.
Among the flights forced to circle in the skies above southern England was British Airways flight BA2957 from Glasgow, which was due to land at 11.05am.
At around midday, the airport said flights had begun again, but passengers were urged to contact their airline for the latest information.
A spokesman for the West Sussex airport said the runway was shut shortly after 10.15am and did not reopen until 11.38am.
According to Gatwick's website at least 19 incoming flights were diverted to other airports, and a number of departing services were delayed.
An airport spokesman said: "Arriving and departing flights recommenced from Gatwick at 11.38am.
"The runway closure has caused some flights to be diverted to other airports in the area and there will be delays to some departing flights.
"Friends and family waiting for passengers should contact the relevant airline for the latest information."
The cause of the spillage has not yet been confirmed, but it is believed to involve a Boeing 747-400 plane.

Many flights were diverted or delayed after an oil spillage at Gatwick Photo: Gatwick Airport
Some passengers took to Twitter to express their upset at being delayed by the spillage:
Gatwick is Britain's second largest airport and is used by more than 40 million passengers each year.
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