Voters in several pivotal states guaranteed Tuesday that Republicans would retain control of the Senate.

Thirty-four Senate seats were up for election, 15 currently held by Republicans and 19 by Democrats. Republicans hold 51 seats in the current Senate. Democrats have 48, along with the support of independent Sen. Jim Jeffords (search) of Vermont.

At 4:20 a.m. EST Wednesday, FOX News projected Republican John Thune (search) the winner over Senate Minority Leader Tom Daschle (search) in South Dakota.

Earlier at 1 a.m., FOX projected Democrat Ken Salazar as the winner in the Colorado Senate race. FOX also projected GOP Rep. David Vitter (search) as the winner in Louisiana, without a runoff needed. Democratic Sen. Ron Wyden (search) was projected as the winner in Oregon.

FOX projected the following as winners at 11 p.m. Tuesday: Republican Richard Burr (search) in North Carolina; incumbent Democratic Sen. Daniel Inouye (search) in Hawaii; incumbent Democratic Sen. Barbara Boxer (search) in California; Republican Sen. Michael Crapo (search) in Idaho; Democratic Sen. Patty Murray (search) in Washington; and Republican Sen. Arlen Specter (search) in Pennsylvania.

At 10:30 p.m., FOX projected Republican Sen. Jim Bunning as the winner of the Senate race in Kentucky, while at 10 p.m., Senate victories were projected for the following incumbents: Sens. Chuck Grassley (search), R-Iowa, Harry Reid (search), D-Nev., and Robert Bennett (search), R-Utah.

At 9:45 p.m., FOX projected Republican Jim DeMint (search) as the winner of the South Carolina Senate race, while at 9 p.m., the following Senate victories were projected: Republican Tom Coburn (search) in Oklahoma; Republican Sen. John McCain (search) in Arizona; GOP Sen. Sam Brownback (search) in Kansas; Democratic Sen. Chuck Schumer (search) in New York; Democratic Sen. Byron Dorgan (search) in North Dakota; and Democratic Sen. Russ Feingold (search) in Wisconsin.

At 8:30 p.m., FOX projected Republican Sen. Judd Gregg (search) the winner in New Hampshire and Democratic Sen. Blanche Lincoln (search) the winner in Arkansas. At 8 p.m., FOX projected the following Senate victories: Republican Sen. Richard Shelby (search) in Alabama; Democratic Sen. Christopher Dodd (search) in Connecticut; Democratic Sen. Barbara Mikulski (search) in Maryland; and Democrat Barack Obama (search) in Illinois.

At 7:30 p.m., FOX projected victories for GOP Sen. George Voinovich (search) in Ohio and Republican Sen. Kit Bond (search) in Missouri. At 7 p.m., FOX News projected winners in the following states: GOP Rep. Johnny Isakson (search) in Georgia; Democratic Sen. Evan Bayh (search) in Indiana; and Democratic Sen. Patrick Leahy (search) in Vermont.

Retirements by Democrats in North Carolina, South Carolina, Georgia, Florida and Louisiana raised Republican hopes of padding their majority. GOP retirements in Illinois, Oklahoma and Colorado stirred optimism among Democrats that they could regain power. Other tight races were being decided in South Dakota, Kentucky and Alaska.

Ticket-splitting was key to contestants' chances — Democratic presidential candidate John Kerry made little or no effort against President Bush in seven of the nine states with the most competitive Senate races.

Whatever the outcome of the party struggle, the large number of retirements translated into at least eight new members of the Senate.

Multimillion-dollar campaigns were commonplace in the most contested races, and the race between Senate Minority Leader Tom Daschle and GOP candidate John Thune in South Dakota set the pace.

To learn more about other key Senate races, click on the headlines below:

Daschle Loses Senate Seat in South Dakota

Republican John Thune, who narrowly lost his first try for the U.S. Senate two years ago, defeated Senate Democratic Leader Tom Daschle of South Dakota.

Martinez Elected to Senate in Florida

Republican Mel Martinez, a Cuban emigre who left President Bush's Cabinet to run for the Senate, narrowly defeated Democrat Betty Castor to complete a GOP sweep in Senate races across the South.

Murkowski Wins Alaska Senate Race

Republican Lisa Murkowski earned a term in the Senate in her own right Wednesday, defeating popular former Gov. Tony Knowles and overcoming the commotion that arose when her father, the governor, appointed her to fill his Senate term.

Vitter Avoids Runoff, Clinches GOP Victory in Louisiana

Rep. David Vitter became the first Louisiana Republican elected to the Senate since Reconstruction, vanquishing four Democrats on Tuesday to capture the seat outright.

Colorado Votes to Send Salazar to Senate

Voters opted for the moderate state attorney general over Republican beer baron Pete Coors and gave the Democrats a seat once thought to be solidly in the GOP column.

Obama Wins Illinois Senate Race

Illinois voters across the spectrum embraced Barack Obama, whose message of optimism and unity made him a Democratic Party superstar, electing him Tuesday over conservative Alan Keyes to become only the fifth black U.S. senator in history.

Bunning Overcomes Challenge From Mongiardo

Republican Sen. Jim Bunning held off a strong challenge by Democrat Daniel Mongiardo to win a second term, scoring a razor-thin victory following a campaign in which the candidates exchanged increasingly sharp personal attacks.

DeMint Wins S.C. Senate Seat for GOP

Jim DeMint latched onto Republican coattails for a victory in South Carolina's open U.S. Senate seat that had been held by Democrat Ernest "Fritz" Hollings for 38 years.

Burr Comes Out on Top in N.C. Race

North Carolinians chose Richard Burr, a Republican congressman from Winston-Salem, above Erskine Bowles, a Democratic investment banker from Charlotte, to replace senior Sen. John Edwards.

Voinovich Wins Re-Election in Ohio

Republican George Voinovich, well-known and well-funded, was easily re-elected to a second term in the U.S. Senate on Tuesday, defeating Democratic state lawmaker and former congressman Eric Fingerhut.

Dodd Wins Historic 5th Term in Conn.

Democratic U.S. Sen. Christopher Dodd became the first Connecticut senator elected by voters to a fifth term, easily beating Republican newcomer and admitted underdog Jack Orchulli.

The Associated Press contributed to this report.