Greece's leftist SYRIZA party and its main rival, conservative New Democracy, have been running neck-and-neck in polls before Sunday's election, making an outright winner unlikely.
Greece needs political stability to implement the terms of a new 86-billion euro bailout, and avoid lurching back towards bankruptcy and an exit from the euro.
Here are some possible scenarios, coalitions and the political risks they entail:
SYRIZA allies with New Democracy.
Such an alliance would secure a strong parliamentary majority in the 300-seat house, helped by the electoral system which gives a bonus of 50 seats to the first party. It would probably please Greece's creditors, who have in the past sought proof of commitment to the bailout by political leaders.
It would be very difficult, however.
New Democracy leader Vangelis Meimarakis says he is open to such an alliance in a last chance to save the crisis-hit country. He says minimum cooperation is needed to form a government plan and has also called for a national negotiating team. But he has accused SYRIZA of “incompetence” in handling the crisis.
Tsipras, struggling to rally disgruntled leftist and centre-left voters, has said it would be an “abnormal alliance”.
He has accused New Democracy of being part of a corrupt political system that helped plunge Greece into the debt crisis.
The two parties are expected to clash on issues such as specifying reforms, leading to delays in their implementation, and on immigration.
New Democracy is in favour of labour market liberalisation, wants a smaller state and tighter border controls to fight illegal immigration. SYRIZA wants collective bargaining to be reinstated, more EU funds and, if possible, voluntary relocation of undocumented migrants.
Another risk is that such an alliance would very likely make the far-right Golden Dawn the main opposition, bringing greater visibility to a movement whose leaders have been charged with setting up a criminal organisation.
Split the bill
New Democracy or SYRIZA with Potami, PASOK.
Although an alliance with only one of the smaller parties, the centrist To Potami (River) or the once dominant Socialist PASOK – may be possible depending on the results, the two leading forces have suggested a wider partnership, for the sake of political stability making such a coalition more likely.
It is estimated that around 38 percent of the vote will be needed for a party to get a ruling majority in parliament.
Meimarakis said that New Democracy would cooperate with pro-euro parties if SYRIZA rejected his offer – hinting at PASOK and To Potami. Tsipras has also left a window open for such a coalition, despite accusing them of links with vested interests.
To Potami, which was founded last year by a former journalist and strongly favours Greece staying in the euro, has said that it is willing to strike a pact with leftists or conservatives. It is taking between 4 to 7 percent in polls.
The ratings of the once powerful PASOK party, which came to power with about 44 percent when the crisis broke out in 2009, have dropped to 4-6 percent.
PASOK participated in governments with New Democracy and smaller parties during the crisis. Its newly appointed leader Fofi Gennimata has said that only through cooperation can politicians pull Greece out of the crisis.
But having bitter experience of fragile coalitions, PASOK may not easily risk its already low popularity.
SYRIZA with the Independent Greeks.
SYRIZA has said it would like to ally with its former coalition partner, the Independent Greeks – who have also ruled out an alliance with New Democracy. But polls suggest the right-wing party may not cross the 3 percent threshold needed to enter parliament.
Neither PASOK nor To Potami would want to ally with them.
ANOTHER ELECTION No one wants one. For one thing, voters are getting weary.
Sunday's national ballot will be the third this year after the national election in January and the referendum on the bailout in July.
Tsipras has already hinted at a blame game if another vote gets called.
He said this week that To Potami and PASOK would need to consider taking the responsibility of a repeat election if they demanded that New Democracy join any coalition with SYRIZA.