Behind the scenes in the corridors of Parliament House, politicians are putting money on the outcome of Wednesday's same-sex marriage postal survey.
The book is being run by Derryn Hinch staffer Glenn Druery, also known as the "preference whisperer" of Australian politics.
Druery told BuzzFeed News it's more of a guessing game than a proper punt. He's taking $5 donations with each guess and the winner has the honour of donating all money raised to the Wintringham specialist aged care charity.
But the bets so far indicate that all politicians – including those who have voted no – are predicting a "yes" result. The average of all guesses is 61.3%.
Education minister and marriage equality support Simon Birmingham put $5 on "yes" to win at 56.2%. Newly elected president of the Senate Scott Ryan has guessed "yes" at 59%. Assistant Minister for Agriculture and Water Anne Ruston also thinks it will be "yes" at 60.5%.
Liberal senator Dean Smith, who will introduce a private members bill on Wednesday if the postal survey is returned "yes", has put his money where his mouth is and donated $5 for "yes" to win at 63%.
Some politicians are hedging their bets with two guesses at the result.
NSW Nationals and anti-marriage equality senator John "Wacka" Williams is predicting "yes" at 56.1% or 57.4%. "No" voter David Bushby is also backing "yes" 59% to "no" 41%.
Labor senator Doug Cameron is the most confident, predicting "yes" by 70%. Fellow NSW Labor senator Sam Dastyari think "yes" by 65%, and ACT Labor senator is going with "yes" by 68%.
On the crossbench Hinch is tipping "yes" by 56%. Liberal Democrat senator David Leyonhjelm thinks 69% "yes".
South Australian senator for the anti-gambling party the Nick Xenophon Team Skye Kakoschke-Moore refused to bet. But her NXT colleague Stirling Griff put $10 down on "yes" to win by either 57% or 62%.
Greens senator Lee Rhiannon put down two votes for "yes" at 58% and 63%. Tasmanian Green Peter Whish-Wilson think "yes" will win by 69%.
Head of the Australian Council of Trade Unions Sally McManus has also put her money where her mouth is, betting the result will be 59.5% "yes".
Many didn't want to guess. Prime minister Malcolm Turnbull's office refused to give a prediction, instead donated $50 and said they were "waiting the peoples verdict".
Opposition leader Bill Shorten's office politely declined two requests to get involved. So did Greens leader Richard Di Natale.
One Nation leader, senator Pauline Hanson didn't want a bar of it, but former One Nation turned independent senator Fraser Anning thinks it will be close but "yes" will take it by 54%.
Druery, a notorious numbers man, says he thinks "yes" will win in the high 50s. When pressed for a prediction he said "yes" with 59.5% of the vote, preferences pending.
"If it did go to preferences, it would get up," he said.