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.