Authors Will Self and Hilary Mantel are neck and neck to win the prestigious Man Booker Prize for fiction on Tuesday evening, according to bookmakers' odds.
Self is shortlisted for the first time for Umbrella, about an epidemic of encephalitis lethargica after World War I which killed almost a million people.
Previous winner Mantel is nominated for Bring Up the Bodies, the second book in her fictional Thomas Cromwell trilogy.
Bookies William Hill said it would be the closest finish ever.
Its most recent odds for Mantel are 6/4, making her the narrow favourite over Self at 2/1.
But Ladbrokes place Self as the favourite at 6/4, ahead of Mantel at 9/4.
Other contenders include Indian poet Jeet Thayil with his debut Narcopolis.
Tan Twan Eng, who was born in Malaysia, has made the shortlist with his second novel, The Garden of Evening Mists.
The book is set in the mountains of central Malaya during the pre-independence turmoil of the 1950s.
Alison Moore's The Lighthouse follows the journey of a middle-aged man who goes to Germany for a walking holiday after his marriage collapses but finds the trip brings back difficult memories.
Swimming Home is Deborah Levy's first novel in more than 10 years. Traditional publishers turned down the novel and it only made it into print following the help of supporters and friends and through the use of subscription.
Chair of the judges, Sir Peter Stothard, said: "This has been an exhilarating year for fiction. The strongest I would say for more than a decade."
Online retailer Amazon said Mantel's novel had been the best-selling shortlisted book on its website since the list was announced on 11 September, followed by Moore's Lighthouse.
Mantel's book accounted for 36% of sales from the shortlist, with Moore's novel taking 20%.
Self's novel has sold the least on Amazon so far, accounting for just 8% of sales.
The impact on sales for a Man Booker winner is considerable - every winning book since 1996 has grossed more than £1m.
Yan Martel's Life of Pi, which won in 2002, made just under £10m.
Mantel's Wolf Hall, which was the winning book three years ago, went on to make £5.4m.
Last year's winner, Julian Barnes's The Sense of an Ending, has sold 300,000 copies so far.
If Mantel wins again, it will be the first time a living British writer will have won the Man Booker Prize twice.
The ceremony takes place on Tuesday evening at the Guildhall in central London.