There are two election battles going on ahead of polling day on July 2. One is for executive power in the contest for the House of Representatives. The other is for the Senate, which is elected under a system of proportional representation that utilises the Single Transferable Vote (STV).

To win a Senate place at a double-dissolution election, a candidate needs to secure 7.7% of the vote cast in the candidate’s state. This sounds like a trifling amount, but in a state like New South Wales, 7.7% equates to 336,963 votes. This, by the way, is the total number of voters in Tasmania, where, to secure a Senate seat, a candidate needs only 25,945 votes.

Trying to predict Senate outcomes is difficult at the best of times, but the 2016 contest for the upper house is even more unknown thanks to the abolition of the group voting ticket, and its replacement by what is effectively optional preferential voting.

Nobody knows how voters will respond to the Australian Electoral Commission’s instructions on filling in Senate ballots. This means there is great uncertainty about how many ballots will end up counting as preferences.

The best prediction that can be made is that, in order to win a seat, candidates will have to rely on achieving a quota or close to a quota on primary votes alone. The days of a Ricky Muir winning a seat because preferences boosted an otherwise miniscule primary vote are probably over.

Assuming that seats will most likely go to party tickets getting enough primary votes to achieve the requisite quota, only five parties are guaranteed representation. Those are Labor, Liberal, Nationals, the Greens, and Nick Xenophon’s new party. The latter’s support in South Australia should see it secure at least two – possibly three or maybe four – seats.

Of the rest, the only former senator who has a reasonable chance of being returned is Jacqui Lambie in Tasmania. It is quite conceivable that a high-profile individual could get the 26,000 votes needed to secure a seat in a state with a history of voting for prominent individuals ahead of party tickets.

There is much less certainty about the fate of the others. Glenn Lazarus and Dio Wang were elected under the auspices of the Palmer United Party, which has since imploded.

Pauline Hanson is running for a Queensland Senate spot, which could be very interesting.

The mystery of why so many people voted for the Liberal Democratic Party (LDP) in New South Wales in 2013 has not really been solved. But the inclusion of party emblems on the ballot paper as part of the recent Senate voting reforms suggests the LDP’s David Leyonhjelm was the beneficiary of mistaken identity and having pole position on the 2013 ballot paper. It is unlikely any of these happy coincidences will happen again.

Given the Coalition will not win an upper house majority, the next most likely scenario is that Xenophon and his party members will hold the balance of power in the Senate. Both major party leaders would probably be comfortable with this outcome.

For all his positioning on populist issues, Xenophon has great experience in the ways of upper house politics, especially with regard to negotiating with the major parties on important legislation.

Xenophon’s track record as a crossbench senator has always been characterised by trying to use the upper house to modify bills rather than simply defeat them. And his political persona has none of the volatility associated with a Clive Palmer or the ideological rigidity of Tasmania’s Brian Harradine, who held the balance of power for a time when John Howard was prime minister.

The unknown factor in this, however, is how Xenophon will fare as the leader of a political party with a parliamentary wing. The history of minor parties put together quickly by prominent characters ahead of a general election has not been a happy one.

The Nuclear Disarmament Party was created ahead of the 1984 election, and imploded soon after. Pauline Hanson’s One Nation did not survive long after its impact on the 1998 Queensland state and federal elections, and the implosion of the Palmer United Party has already been alluded to.

The challenge for Xenophon will not necessarily be about winning Senate seats, but keeping his party together in the transition from being a support mechanism for a charismatic leader to being a parliamentary party.

All of this assumes the Nick Xenophon Team will hold the balance of power in the Senate, and this is by no means a certainty. Any candidate from a party other than Labor and the Coalition could be pivotal to the balance of power in the Senate. A Labor-Green majority cannot be ruled out either.

The chances of another minor party being in such a position of power is remote, not least because of the new Senate voting rules that do away with preference harvesting. This is a reform that Xenophon himself was instrumental in expediting, showing once again how effectively he can merge his political self-interest with declarations that he seeks to serve the national interest.

Nick Economou does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.