UPDATE 12:35 a.m. Mitt Romney has outdueled Rick Santorum in Ohio, claiming the hotly contested, pivotal Super Tuesday state.
Romney did best in Ohio metropolitan areas, as well as among voters worried about the economy and making sure the GOP nominated the best candidate to defeat President Barack Obama.
The former Massachusetts governor had nearly 38 percent of the vote with 97 percent of precincts reporting unofficial returns. Santorum was sixth-tenths of a percentage point behind at 37.2 percent. Romney prevailed in another November swing state to bolster his front-runner status over the former Pennsylvania senator.
Former House speaker Newt Gingrich was third, at 15 percent, in the state that lies between Romney's native Michigan and Santorum's home state. Texas Rep. Ron Paul, who largely bypassed Ohio, was running fourth at 9 percent.
UPDATE 11:38 p.m. Mitt Romney has edged past Rick Santorum in Ohio with the last precincts still coming in for the hotly contested, pivotal Super Tuesday state.
Romney led by 1,837 votes with 85 percent of precincts reporting unofficial returns. The former Massachusetts governor had 37.6 percent of the vote to 37.2 percent for Santorum.
Santorum hoped to rejuvenate his bid to overtake Romney for the Republican presidential nomination by claiming his biggest primary prize yet, while Romney hoped to add another key November swing state to bolster his front-runner status.
Former House speaker Newt Gingrich was a distant third, at 15 percent, in the state that lies between Romney's native Michigan and Santorum's home state. Texas Rep. Ron Paul was running last at 9 percent.
UPDATE 10:46 p.m. Republican presidential candidate Rick Santorum maintains a slight lead in Ohio over challenger Mitt Romney.
Seventy-five percent of precincts have reported results.
Santorum has 38 percent of the vote. Romney has 37 percent.
UPDATE 10:16 p.m Sixty percent of Ohio precincts are reporting results in the Republican race for the presidential nomination.
Rick Santorum maintains a slight lead over Mitt Romney. Santorum has a reported 38 percent of the vote, while Romney trails just two percentage points behind, with 36 percent of the vote.
Meanwhile, Romney is declaring "I'm going to get this nomination" as Republicans in 10 states had contests to pick a challenger to President Barack Obama.
Romney on today congratulated rivals Newt Gingrich for his win in home state Georgia and Santorum for wins in Oklahoma and Tennessee. Contests are still going elsewhere on the single largest day of voting so far in the nominating battle.
Romney is telling supporters that it's been a long road getting to Super Tuesday and, in his words, "my opponents have worked very hard."
Romney is keeping most of his election night remarks honed on Obama, again criticizing the incumbent he wants to vote from office in November. He warns supporters that Obama would be "unrestrained" if he wins a second term and would trample Americans' freedoms.
UPDATE 9:51 p.m. With 37 percent of precincts in Ohio reporting, GOP candidate Rick Santorum takes a slight lead over his opponent, Mitt Romney. Santorum has 39 percent of the vote, while Romney has 36 percent.
Santorum says "this was a big night tonight" and is calling the day's biggest race in Ohio "too close to call."
Santorum today told supporters that "we're going to win a few and we're going to lose a few." But he delivered his remarks in a congressional district where he didn't appear on the ballot, underscoring the challenges facing his ragtag campaign.
Santorum was heavily outspent by his rivals and he says his campaign "went up against enormous odds." He says he overcame obstacles and vowed to continue his campaign to defend liberty.
UPDATE 8:47 p.m. In early poll numbers, two Republican presidential hopefuls are neck and neck for the lead. Mitt Romney has with 38 percent of the vote, as does Rick Santorum.
Only 6% of Ohio's 9,440 precincts have reported numbers since polls closed at 7:30 p.m.
Early results from an exit poll of Republican primary voters in Ohio find a candidate's ability to defeat President Barack Obama is the most important quality guiding their decisions. The survey also finds nearly two-thirds of voters saying they're committed to backing the eventual Republican nominee, no matter who wins the primary.
About four in 10 called a candidate's ability to defeat Obama the most important quality guiding their decisions.
Just about three in 10 voters say this year's campaign was more negative than previous presidential contests. Most said it was about the same and one in seven called it more positive.
Preliminary results from the Ohio exit poll include 1,848 voters. The survey's margin of sampling error is plus or minus 4 percentage points.