THE Senate is set to move sharply to the left, with the Greens winning a Senate seat in every state, and Labor taking a Coalition seat in Tasmania.

The Greens will have the balance of power to themselves when the new senators take up their seats on July 1, 2011. That means no legislation will pass the Senate without support from at least two of the three main parties: either Labor and Greens, Coalition and Greens, or the Coalition and Labor.

The Coalition lost at least two seats on Saturday, possibly three. The one seat in doubt is the last seat in Victoria, where Liberal senator Julian McGauran is in a three-way battle with the DLP's John Madigan and Family First senator Steve Fielding.

On Saturday night's figures, ABC analyst Antony Green's Senate calculator suggested the DLP would win the seat on a stack of preferences. But only a small shift of votes would give the seat to Senator Fielding. And the likely Liberal gains as postal votes are counted mean that despite the current figures, Senator McGauran probably has the best chance of all.

In most states, the six Senate seats being contested divided 3-2-1 between the Coalition, Labor and the Greens. That is the outcome in NSW, Queensland, WA and South Australia, and the most likely outcome in Victoria.

In Tasmania, the collapse of the Liberal vote cost Senator Guy Barnett his seat, with the Coalition winning two of the state's six seats, Labor three and the Greens one.

It is the second election in a row that Labor and the Greens have won four seats between them in Tasmania, and it guarantees them a clear majority in the Senate for any legislation they agree on.

In other results:

■ The Greens took a Senate seat from the Coalition in Queensland, where the freak vote in 2004 saw the Liberals win four of the six seats between them.

■ The Greens took seats from Labor in both NSW and South Australia.

■ In the ACT, Liberal senator Gary Humphries narrowly withstood a record Greens vote to keep his seat.

Saturday's vote will bring to an end the six years of Coalition dominance of the Senate - first with 39 seats and a majority of its own, and more recently, with 37 seats and Senator Fielding as a regular ally.

The new 76-member Senate will have 34 Coalition senators, 31 Labor, nine Greens, South Australian independent Nick Xenophon, who was not facing re-election, with the last Victorian seat still in doubt.

Part of the Greens' success was due to its support from the Australian Sex Party. It won 2 per cent of the vote nationwide, almost matching Family First's 2.1 per cent, and all those went to the Greens.

The Greens' own vote was a record 13 per cent nationwide, and their final vote after preferences is likely to be around 2 million, making them the largest third party we have seen. The Greens polled 23 per cent of the vote in the ACT, 20 per cent in Tasmania, 14 per cent in Victoria and WA, 13 per cent in Queensland and South Australia, and 10.4 per cent in NSW.

After Victoria, the next closest contest was in New South Wales, where the Greens put up their NSW leader, former communist Lee Rhiannon.

NSW voters faced a very congested ballot paper, with 80 candidates from 33 groups. Much of that was due to builder and serial candidate Glenn Druery, running this time for the Liberal Democrats, who organised preferences for himself from 15 other groups.

While he polled just 2 per cent of the vote, Antony Green's calculator suggests preferences would lift that to 8.2 per cent before he was eliminated.

Two old parties, the Australian Democrats and One Nation, crumbled into insignificance. After Family First and the Sex Party, the next biggest votes went to the Shooters Party and the Liberal Democrats, each with 1.6 per cent.