Opinion polls, the last before polling day, put the opposition Socialist Party ahead, albeit without a clear majority. But with up to 20 per cent of voters still undecided, and opinion polls notoriously unreliable, few are betting on the outcome.
The daily Publico predicted the Socialist Party would win 40 per cent and the ruling Social Democratic Party 35 per cent. Battling for third position are the far-right Popular Party, with a possible 10 to 11 per cent, and a green-Communist alliance, the United Democratic Coalition (CDU). Expresso magazine gives 44.5 per cent to the Socialists, 32.7 per cent to the Social Democrats, and 11.5 per cent to the left.
The Socialist leader, Antonio Guterres, boosted his party's chances in two spirited television debates with his Social Democrat counterpart, Fernando Nogueira, who is considered trustworthy but short on charisma. Both promise to create more jobs. Unemployment, although relatively low at 7 per cent, has risen sharply in the past two years and is top of the list of voters' worries.
Mr Guterres, shunning the government's free-market Thatcherism, has been campaigning "with his heart" - the Socialist slogan - to win over the unemployed who once flocked to Alvaro Cunhal's Communists but who have abstained or voted Social Democrat in recent years.
Under the retiring Prime Minister, Anibal Cavaco Silva, who won thumping victories in 1987 and 1991, Portugal enjoyed nearly a decade of stability and prosperity, coinciding with EU membership.
But in the past two years it has suffered from the recession that swept the rest of Europe and after 10 years the government is looking tired and bereft of ideas.
But the Socialists have failed to seize a commanding position, and the Social Democrats are hammering home the message that the worst is over and they offer the best chance for recovery. Mr Cavaco Silva has broken his promise to keep aloof from the campaign, and has come out of his tent to rally the troops, reflecting the closeness of the expected result.
On the main issues, a commitment to a European single currency by 1999 and to economic recovery generally, there is little to choose between the two big parties. This could pose a problem if the winner has to contemplate a post-election coalition. The Socialists' possible partners, the Communists, are fiercely Euro-sceptic, as are the Social Democrats' likely allies, the Popular Party.
The Socialists say they will go it alone in a minority government, relying on the Communists for key votes without a formal pact. The Social Democrats have given the nod to the Popular Party, which is eager to share power with whoever comes out on top.
Mr Cavaco Silva said in February he would step down as Social Democrat leader after the election, a decision interpreted as a possible step towards standing as a candidate in next year's presidential contest. It is thought he sought to withdraw from the front line with his reputation intact and avoid being harmed by a possible reverse for his party on Sunday.