William Hill on Friday cut odds on humans making contact with other forms of intelligent life on or before January 1, 2000 to 33-1.
William Hill spokesman Graham Sharpe said: "We've been lowering the odds over the past couple of months."
They were 1,000-1 at one point, before falling to 100-1.
"There was all the excitement about possible life on Mars, and now speculation about what lies beneath the seas on Jupiter's moons," he said.
It was also possible that proof may already exist but not have been officially announced by governments.
"People are beginning to accept that there is more and more out there, that more is known than has been given public airing."
Original file name: CNI - Odds on ET Life
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