MANNING, N.D. (AP) -- Shirley Meyer grew up on a ranch north of Dickinson, N.D., and has represented her rural district in the state House for a decade. But when she knocks on doors in her re-election campaign, she sometimes feels like a stranger in her own home.
"I was just shocked at how many new people there were," Meyer said during a recent campaign swing through a south Dickinson mobile home park. "I didn't see one North Dakota (license) plate."
The oil boom that has transformed North Dakota's economy and reshaped the rolling prairie landscape has also added an element of mystery to next week's election by adding thousands of potential new voters to the region's tiny electorate. And the political suspense is tied to the national question of which party controls the Senate in January.
North Dakota's contest is one of several states with Senate contests that have remained tied for months, with no signs of clarifying before Tuesday's election. A handful of them, such as Montana's Senate race one state west, may not even be resolved then.
Republicans are still looking to gain four seats they need to win the Senate majority if President Barack Obama wins reelection, three if GOP presidential hopeful Mitt Romney prevails.
Workers from all over the country have pouring into western North Dakota for jobs in the booming Bakken oil shale region. Dickinson, a city of 16,000 that didn't grow at all between 1990 and 2000, is now surging past 20,000 residents, with acres of new temporary housing. By one state measure, the number of oilfield workers has increased from 5,600 to 14,000 since the last presidential election. And many of the new arrivals are eligible to vote.
What that means for North Dakota politics, or individual candidates, is anyone's guess.
"I'm just hoping that I have enough ballots," said Joan Hollekim, the county auditor in Mountrail County, North Dakota's biggest oil producer. She increased her ballot printing order by 25 percent, and already has more than 600 early votes, a record.
Beth Innis, the auditor in neighboring Williams County, said she's already booked more than 2,500 absentee votes, which is double what she expected.
"I thought it would be big," Innis said of the rising number of voters. "I didn't think it would be this big."
In North Dakota, the only state that does not have voter registration, any citizen over 18 who has lived in the same place for at least 30 days can cast a ballot. That would include oilfield workers who may actually be living elsewhere and commute home to see their families.
Democrat Heidi Heitkamp and Republican Rick Berg are both pitching hard for the votes of North Dakota's energy workers. In a final campaign swing this week, Berg visited an oilfield trucking service company, a natural gas processing plant and a coal mine in western North Dakota.
Heitkamp talks up her advocacy for North Dakota's oil and coal industries when she served as state attorney general and tax commissioner. In one of her television ads, she speaks over the noise of a passing train of oil tanker cars while promising to support development of a new North Dakota refinery to process crude.
The oil industry is making sure its work force knows how to participate. A recent newsletter from the North Dakota Petroleum Council instructed workers who live in recreational vehicles or "skid shacks"— tiny huts, often no larger than a single-car garage, which can be hauled on flatbed trailers — how to request mail ballots.
The Brighter Future Alliance, a nonprofit group with ties to prominent North Dakota Republicans, has conducted voter information workshops in several of the temporary housing camps dotted throughout western North Dakota.
"We have focused on what we think is a critical thing for the country, and that is to pursue domestic energy supplies..." said Shane Goettle, an alliance official and former aide to Republican Sen. John Hoeven. "I think they can well be motivated to show up."
It's unclear how many new workers will vote.
Patty Caldwell, who started cleaning trailer houses at North Dakota oil well drilling sites more than a year ago to stave off foreclosure of her home in Oregon, said she wanted to make her voice heard.
"I just figured that I'm part of this community now," said Caldwell, whose company is in New Hradec, a hamlet about 10 miles north of Dickinson. "I have friends here. There's issues that I'm concerned about."
Monty Leonard, who drives a truck for a company that hauls water for the oil industry, came here from Oklahoma two years ago. He is casting his first vote in North Dakota.
Leonard said he has been following the presidential campaign, but is not familiar with the North Dakota candidates.
"I haven't been here very long, so I don't know the people," Leonard said of the candidates.
The potential magnitude of the oilfield vote — if it votes — is clearly visible. Across the area, rows of temporary trailers are plunked in the middle of brown, treeless pastures, while smoke-belching earth movers prepare space for new housing developments and business construction.
This year, as many as 4,300 new voters have been added to a state voter database in the nine largest oil-producing counties. That's more people than live in 26 of North Dakota's 53 counties, and a significant number in a state where 160,000 votes could elect either Berg or Heitkamp in their closely fought race.
Almost 533,000 North Dakotans are eligible to vote, a 7 percent increase since the last presidential election, the state Commerce Department says.
Meyer, a Democrat, said she has tried to "hit the new areas" in her re-election campaign.
She said some of the workers had absentee ballot paperwork.
"The vast majority of them that I visited with said, 'We work 16 hours a day, and we have no intention of voting" in North Dakota, she said.
Other lawmakers said they doubted the new residents would be rushing to the polls.
"I don't think they're going to influence (election results) a lot for the local stuff. They're really just doing their work, and sending money home to their families," said state Rep. Bob Skarphol, a Republican from Tioga.