Liberal Democrat Stephen Kearney is the only candidate likely to beat the Conservatives in the race to succeed Tory Boris Johnson as south Oxfordshire MP, according to Ladbroke's bookmakers.
They have put the parliamentary hopeful at 6-1 to win the by-election on Thursday, June 26.
The Liberal Democrats came second at the General Election, but Mr Johnson still had a majority of almost 13,000.
Ladbrokes see Mr Kearney as the clear challenger to Conservative John Howell and have rated Labour candidate Richard McKenzie's chances at 100-1 to win the election.
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