Although the Social Democrats scored fewer votes than the Christian Democrats, it can win extra seats. Tipping the scales are so-called "overhang" seats, which derive from the two votes that each German casts when he goes to the polls.

In the first vote, the candidate with the most votes in each constituency is elected to one of 299 seats -- half of the 598-seat Bundestag chamber.

Keeping the extra seats

The second vote decides the allocation of the other 299 seats via the state lists using a proportional system of calculation. Those seats are distributed based on the number of votes obtained by party lists, with people at the top of their lists having the best chance of getting in.

Overall, it means a party can win seats individually and as a group, and if there is a difference in the number obtained under either system, the party is allowed to keep the extras, which are known as the "overhang" seats.

As a result, the Bundestag elected at the last general election in 2002 had a total of 603 instead of 598 seats. Once the Bundestag has been chosen, the federal chancellor is elected with an absolute majority of parliamentary votes.

Dresden the decider?

Who takes power could first be decided in two weeks, when one district Dresden heads to the polls. The district in the East German city will vote on Oct. 2 this year because a candidate for the right wing National Democratic Party (NPD) died suddenly during campaigning last month -- causing a re-scheduling. In voting Sunday, the city's second district voted CDU.

Experts say Dresden could decide as many as three Bundestag seats. With the SPD estimated to get 222 or 221 seats, and the CDU/CSU between 224 and 225 seats, the district could decide whether Schröder or Merkel takes power, should the two major parties form a "grand coalition" with one another.