The Scottish Green Party could nearly double its tally of MSPs at next May's Holyrood elections, a conference gathering has been told.
The party currently has seven MSPs at Holyrood
Party co-convener Robin Harper claimed the current seven MSPs could go up to between 10 and 15.
He also warned that the party would drive a hard bargain if it found itself holding the balance of power.
Mr Harper was speaking on Saturday, on the opening day of his party's annual conference in Edinburgh.
The Greens do not rule out a coalition but are studying the detail of a scheme used by minority parties in other countries.
This would involve the Greens supporting another party - in return for concessions to Green policies.
Their sole pre-condition would be a requirement for the other party to rule out any new nuclear power stations.
Mr Harper reminded the conference he had accurately predicted that the Greens would see between five and 10 Green MSPs returned in the 2003 Holyrood election.
He said: "This time, I really will be disappointed and surprised if we got less than 10.
"And we are probably and possibly on line, in the best of circumstances, to get up to 15 - and what a position that would be."
Mr Harper argued that the party had now entered mainstream politics in Scotland and was "a serious player" in Holyrood.
Robin Harper is co-convenor of the party
He said: "Now we are a force to be reckoned with.
"Just like Green parties across the world we are recognised as a party that can take on government and get things done."
He pointed to the track record of Green MSPs on issues ranging from ID cards to dawn raids on families of failed asylum seekers, planning appeals, motorways and climate change.
Mr Harper claimed rival parties were not serious about environmental issues and declared: "We will not just get the support of those who want serious action on environmental issues.
"People are becoming more aware than ever that the Green Party stands for so much more."
He told the conference: "We could hold the balance of power and we will take this responsibility seriously.
"We're not in it to prop up a government.
"We want serious influence and change, and we'll demand it if we are given the opportunity."
He went on: "We may have been the conscience of the first parliament - this time round we will be the driving force of change in the parliament.
"We will drive a hard bargain, given the chance."