Since the last opinion poll in October, support for Mona Sahlin's party has grown by 1.3 percentage points to 40.4 percent.
The Social Democrats' opposition partners however both lost support for the third poll in succession. The Left Party dropped 0.2 percentage points to 5.6 percent, while the Green Party fell back 0.6 points to 6.2 percent.
The opposition parties' combined results (52.2 percent) give them a commanding lead over the four parties of the centre-right government (42.6 percent).
Of the government parties, only Fredrik Reinfeldt's Moderates saw a rise in support since October, up 1 point to 23.9 percent.
The Christian Democrats remained unchanged at 4.7 percent.
The Centre Party (6.7 percent) shed 1.6 points, a fate shared by the Liberals, down 1.5 points to 7.3 percent.
The Sweden Democrats meanwhile witnessed a surge in support since the last poll, gaining 0.9 points to put them just below the four percent needed for a place in parliament at 3.7 percent.
Skop's poll was based on a December survey of 1,000 potential voters. All changes in the poll are statistically significant, except those for the Centre Party and Liberals.