A new survey from Statistics Sweden has shown that the Social Democrats and the Left Party would account for a combined 51 percent of the votes.
The Social Democrats and Greens could also assemble a majority government if current trends prevailed until the next general election.
The four parties in the ruling centre-right alliance - Moderates, Centre Party, Liberals and Christian Democrats - have dropped 8.3 percent since last year's election to a combined total of 39.9 percent.
Support for Sweden's largest party, the Social Democrats, has grown by 10.9 percent since the 2006 election.
The survey was based on telephone interviews with a random sample of 9,383 voters carried out from October 29th to November 25th.
Statistics Sweden November party preference survey (Changes since May in parentheses)
Moderates 22.6 (-1.3)
Centre Party 6.2 (-0.3)
Liberal Party 6.5 (+0.6)
Christian Democrats 4.6 (+0.2)
Social Democrats 45.9 (+1.0)
Left Party 5.1 (+0.2)
Green Party 5.2 (-0.3)
Others 3.9 (-0.1)