Democrat Jeff Merkley holds a narrow lead over incumbent GOP Senator Gordon Smith this morning with a large block of votes left uncounted from Oregon's most liberal county.

Both Merkley and Smith said the winner of the race likely wouldn't be known until more votes were tallied later today.

The outcome of Oregon's race was being watched closely by both national parties. Democrats increased their majority in the Senate to 56 seats Tuesday, but Republicans managed to stop a complete sweep.

Oregon was one of four Senate races involving Republican incumbents that hadn't been decided.

With nearly 43 percent of the vote counted, Merkley had 47.4 percent of the vote to Smith's 47 percent. But still to be counted were the bulk of the votes from Multnomah County, where Merkley was expected to pick up substantial support.