By Political Writer Peter Wilson
There is a strong feeling around parliament that the gay marriage bill will pass its first reading.
It almost certainly will, but unless there is a strong majority that is not going to mean it will almost certainly become law.
Conscience votes are difficult to predict because there are 121 wild cards in the pack.
MPs vote without any instructions from their parties, and some of them change their minds between first and third readings - the final stage of a bill that puts it into law.
The gap can be up to a year, even longer if the government isn't interested in pushing a bill through, and MPs are going to face intense lobbying.
A select committee will spend at least six months taking public submissions on the bill, and already some MPs - including Prime Minister John Key - are saying they will wait to see how that pans out before deciding their position.
Others take the line that they will back the bill on its first reading "because the debate needs to take place" but they will not commit themselves beyond that.
They are playing it safe. If public opinion turns against gay marriage they can say "the country isn't ready for this" and oppose the bill, hoping they will keep most of their voters happy.
Opinion polls have shown a change in public opinion, with a majority of voters now supporting gay marriage, but the figures are not sufficiently conclusive to give MPs a feeling of security.
In 2004, 40 per cent were in favour and 54 per cent opposed, in 2011 60 per cent were in favour and in May this year that had increased to 64 per cent.
A few MPs have taken firm positions, including all 14 Green MPs who are going to back the bill all the way through.
Most of Labour's 34 MPs are expected to support their colleague Louisa Wall, who drafted the bill.
National has 59 MPs, and the bill's fate is going to be decided by how many of them support it through to its third reading.
The Maori Party's three MPs appear to back the bill, NZ First will probably split its votes, ACT's John Banks will almost certainly oppose it and Mana's Hone Harawira is in favour of it - although he was not a month ago.
Comparisons are being made with the Civil Union Bill, because it is the only similar legislation parliament has dealt with.
Those comparisons are valid, but only up to a point.
The bill was passed 65-55, but of those 120 MPs only 31 are still in parliament.
Times change, and so do the attitudes of politicians.
John Key voted against the Civil Union Bill, but now he "doesn't have a problem" with gay marriage.
United Future's Peter Dunne opposed the Civil Union Bill, but he will vote for the gay marriage bill on its first reading.
Maori Party co-leader Tariana Turia did not want civil unions, now she says the sexuality of parents "isn't the most important thing".
These shifts are leading to forecasts that the bill will succeed, but there are an awful lot of MPs who have not yet declared their hand even on the first reading.
The Civil Union Bill had a first reading majority of 15 and a third reading majority of 10.
If the gay marriage bill has a first reading majority between 15 and 20, it will almost certainly be safe.
More than 20 and it's a slam dunk.