OKLAHOMA CITY (AP) Four Democrats will challenge President Obama in Tuesday's presidential preferential primary, and some pundits predict it's possible Oklahoma could be the first state where someone other than Obama picks up a Democratic delegate.

Under Oklahoma Democratic Party rules, any candidate can win a share of delegates if they receive 15 percent of the vote either statewide or in any one of Oklahoma's five congressional districts.

Early voting began in Oklahoma on Friday and continues Saturday from 8 a.m. to 1 p.m. and Monday from 8 a.m. to 6 p.m. at county election boards. Oklahoma is one of 10 states participating in Super Tuesday elections, when polls will be open statewide from 7 a.m. to 7 p.m.

"There is a possibility that Oklahoma may elect delegates that are not for President Obama," said Ben Odom, a Democratic strategist and former vice-chairman of the Oklahoma Democratic Party. "If there was only one person on the ballot against Barack Obama, they almost certainly would.

"The bottom line is there is some dissatisfaction with Obama in the Democratic electorate, people who for one reason or another are unhappy."

Besides Obama, the four Democrats appearing on the primary ballot in Oklahoma are: Darcy Richardson of Florida, Bob Ely of Illinois, Randall Terry of West Virginia, and Jim Rogers of Midwest City.

Republicans appearing on the ballot in Oklahoma are U.S. Rep. Michele Bachmann of Minnesota, former House Speaker Newt Gingrich, former Utah Gov. Jon Huntsman, U.S. Rep. Ron Paul of Texas, Texas Gov. Rick Perry, former Massachusetts Gov. Mitt Romney, and former U.S. Sen. Rick Santorum of Pennsylvania. Bachman, Huntsman and Perry have dropped out since the filing period.

Of the four GOP candidates still in the race, Romney visited Oklahoma late last year, and Gingrich, Santorum and Paul all campaigned in recent weeks.

While Republicans are seeing a flurry of activity as four remaining GOP presidential candidates scramble to claim victory in this bastion of conservative politics, at least one Democrat on the ballot is hoping to tap into anti-Obama sentiment in the only state in the country where Obama failed to win a single county in 2008.

"I'm all in for Oklahoma," said Terry of West Virginia.

Terry, 52, who has spent the last ten days campaigning in Oklahoma, said he has spent $40,000 in Oklahoma on anti-Obama television ads that feature graphic images of aborted fetuses. The founder of the anti-abortion group Operation Rescue, Terry also has a fundraiser and a rally planned in Broken Arrow Saturday featuring conservative pundit and talk show host Ann Coulter.

Terry acknowledged it would be difficult for him to get the 15 percent needed to pick up a delegate, but he said voter antipathy against Obama, even among Democrats, is palpable in Oklahoma.

"I've never seen so much open hostility and contempt for this president from his own party," said Terry, who also is appearing on the ballot in 10 other states. "These people are angry."

Wallace Collins, the chairman of the Oklahoma Democratic Party, acknowledges the anti-Obama sentiment in Oklahoma, but said it would be difficult for any Democrat to muster 15 percent of the vote, especially with four candidates besides Obama on the ballot.

"I would be surprised if they do," Collins said. "Simply getting a delegate would be a big stretch.

"A lot of the Democrats are not even going to know we're having a primary."