Israel's busiest airport was brought to a standstill early on Tuesday as a test revealed airline fuel was contaminated.
El Al jets were not allowed to leave for hours
Thousands of passengers were delayed for hours as departures from Ben Gurion airport in Tel Aviv were suspended.
Six planes from El Al, Israel's national carrier, were kept on the ground, while other companies were told to refuel elsewhere.
It is thought some planes may have flown with the polluted fuel before it was discovered to be faulty.
The cause of the contamination was unclear.
"We don't know, we are checking now," El Al spokeswoman Liat Peleg told Reuters.
Israel's Haaretz newspaper said the fuel contained dirt, and may possibly have been watered down.
Sub-standard fuel can cause serious engine trouble, and jeopardise flight safety, it said.
"A standard check made on Monday evening by the Israeli fuel companies... showed that the fuel delivered to all airlines taking off from Ben Gurion Airport was polluted and does not meet international standards," Ms Peleg said.
"The fuel companies therefore decided not to deliver fuel to flights taking off from Ben Gurion until clean fuel can be delivered. El Al flights as well as flights of other airlines will therefore be delayed."
The airport began clearing the backlog of flights when arrangements were made for El Al flights to stop and refuel in Larnaca, Cyprus or Antalya, Turkey.
Other airlines were advised to stop and refuel on their way into Israel - causing delays to flight arrivals as well as departures.