Queensland's voting system seems set for change after the July 15 state election.

The current optional preferential voting system -- introduced just before the 1992 state election -- is facing increasing opposition within the ALP, the Liberal and National parties, and even disinterest by the Australian Democrats.

With the Queensland Greens now the only party actively supporting it, major

party sources and a Queensland political analyst say the system will be abolished within two years when the government reviews the Elections Act.

Currently, voters at Queensland elections need only 'vote 1' for their preferred candidate. They can optionally support a second, third, or fourth candidate -- unlike in federal House of Representatives elections where voters must number all squares.

Optional preferential voting was first introduced in Queensland in 1893, abolished during World War II, then reintroduced in 1992 following a recommendation by the Electoral and Administrative Review Commission.

It aims to give voters more ways of expressing their intentions by allowing them to allocate or withhold preferences as they see fit. The commission said: "Encouraging voters to express preferences is ultimately a matter for candidates and parties, and not the electoral system".

However Griffith University political analyst Dr John Wanna said it was now "odds on" the system would be dropped again, particularly as in 1995 it had been used to tactical advantage by the Queensland Greens.

"It may give voters more ways of expressing their views, it may give minor parties increased bargaining power when they threaten to withhold preferences, but its wild-card effect is a nuisance to the major parties who will combine forces to eliminate it."

Optional preferential voting is also used in NSW. Abolishing it there would require a referendum, but in Queensland the system can be changed by an Act of Parliament.

Opposition leader Rob Borbidge said he wanted the system abolished and compulsory preferential voting reinstated.

"Optional preferential voting can effectively be a first-past-the-post system where someone can be elected with less than 50 percent of the vote."

And a spokesperson for Premier Wayne Goss could not guarantee the system would remain beyond this election.

"The operation of the Electoral Act will be reviewed after this election ... we are not in a position to preempt the outcome of that review."

ALP campaign director Mike Kaiser said optional preferential voting gave supporters of minor parties the choice of opting-out of deciding the government.

"It provides a choice for Labor, a choice for the Conservatives, and a choice not to decide ... it has as many dangers for the opposition as for the government.

"It's also a problem for voters having one system at state level, and another at federal level."

Australian Democrats campaign director Tony Walters said the Democrats too held reservations. In this election Democrat supporters were being asked to fill-in all squares on the ballot paper, he said.

"We wouldn't be sorry to see it go, particularly if the system led to a de facto first-past-the-post result."

However Queensland Greens deputy convener Drew Hutton said it allowed voters not to support parties they did not like.

"It means we can tell our voters that we don't think either side is worth supporting."

Mr Hutton and Mr Walters said the Green and Democrats' preferred electoral system was proportional representation.

At the 1992 state election, optional preferential voting helped split the conservative vote -- an average of 13 percent of National Party voters and 16 percent of Liberal voters failed to nominate a second preference in seats surveyed by the electoral commission.

National Party state director Ken Crooke said the Coalition's decision to field a single candidate in each seat except Barron River was "partly motivated" by concern of another split vote caused by optional preferential voting.

Dr Wanna said 'three-cornered contests' between Liberal and National candidates could resume when the system was dropped, particularly in seats where the Liberal and National parties attracted a similar primary vote.