The front-running parties say they will form a coalition, which polls suggest could control two-thirds of Poland's parliament. But it remains unclear if pro-market economic liberals devoted to reducing state bureaucracy, or a socially conservative party determined to preserve welfare-state protections, will emerge with the upper hand.
The pro-market Civic Platform had 34 per cent support in a poll published on Friday, ahead of the conservative Law and Justice party on 29 per cent. But an earlier survey gave Law and Justice a slight edge, suggesting Poland could mimic Germany, where voters last weekend got cold feet about pro-market changes at the ballot box.
The poll gave the governing Democratic Left Alliance only 4 per cent. The party came to power with 41 per cent support in 2001, but its popularity has plummeted amid a string of scandals and its failure to tackle the EU's highest jobless rate, now nearly 18 per cent.
If the outcome is very close, the choice over who will be prime minister could be complicated by the fact that Poland also faces presidential elections on 9 October, with a likely run-off vote two weeks later. Warsaw's mayor Lech Kaczynski, the identical twin brother of the Law and Justice leader, Jaroslaw Kaczynski, is one of two leading candidates in the presidential race.
Jaroslaw Kaczynski has said that if his brother becomes president, he would renounce the premiership in order to spare Poland the confusion of two major leaders who look alike. A Law and Justice victory on Sunday could thus leave Poland in a state of limbo, waiting to see who would become president, and consequently, prime minister.
Having the Kaczynskis in power would probably mean a tougher line towards Russia, with whom relations recently have been strained. In late summer, children of Russian diplomats were mugged in Warsaw, an incident which brought a harsh reaction from the Kremlin and which was followed by attacks in Moscow on two Polish diplomats and a journalist.