The Republican primary will be the race to watch in the ruby red state, where Democrats have virtually no shot at making a pickup. GOP voters will decide their nominee on June 24. If no candidate gets a majority, an Aug. 26 runoff will settle things.
So who are the names to watch? To begin with, look to the state's congressional delegation, where three House members are drawing attention: Reps. James Lankford, Tom Cole and Jim Bridenstine.
Cole, an ally of House Speaker John Boehner (R-Ohio), has been in office the longest. That gives him an organizational leg up on other potentials, strategists say.
"Most people would say Cole [has the inside track] because he's got the machinery, the strategy, and a [mindset] of winning elections," said Gretchen Hamel, a Republican strategist who worked for former congressman J.C. Watts (R-Okla.).
At the same time, Hamel said, Cole may be seen as too moderate in a Republican primary. So might Lankford. Just ask the the anti-tax Club For Growth, known for meddling in Republican primaries.
“We do not know who will run for Sen. Coburn’s seat, but we do know that Sen. Coburn has an outstanding 96 percent lifetime score on the Club for Growth’s congressional scorecard and is a champion of economic freedom," said Club for Growth spokesman Barney Keller. "On the other hand, Congressman Lankford has a lifetime 78 percent, and Congressman Cole has a lifetime 73 percent, both of which are obviously substantially different from a score in the 90s."
House GOP leaders are anticipating that Lankford -- a junior member of the leadership team -- to jump into the race, according to a senior aide. While he was elected with the raucous class of 2010, Lankford has remained a close ally of senior Republicans, particularly Rep. Paul Ryan (R-Wisc.).
Bridenstine would be able to carry the tea party mantle if he runs. He's in his first term on Capitol Hill after defeating an incumbent in a 2012 primary.
Rep. Frank Lucas (R-Okla.) is another name to watch. But he would have to give up a powerful spot as chairman of the House Agriculture Committee to make a bid, which may prove too high a cost.
Beyond Congress, another name being mentioned is Attorney General Scott Pruitt. Pruitt ran for Congress unsuccessfully in 2001.
Ed Goeas, a Republican pollster who has worked for many of the potential candidates in some capacity and polls for Gov. Mary Fallin (R) said he thinks that Pruitt and Lankford appear likeliest to get in the race. Goeas said he was speaking in his own capacity and not for Fallin.
"I think in terms of the two who are almost definitely going to get into it: James Lankford and Scott Pruitt," he said.
Republicans also mentioned state House Speaker T.W. Shannon (R), a former Cole aide, as a name to watch, if Cole doesn't decide to run. Former governor Frank Keating (R) is another name to keep an eye on.
Coburn's departure means two Senate elections and a gubernatorial race in Oklahoma this year. Fallin and Sen. James Inhofe (R) are expected to win in November.
The on-year special election adds an extra element to the race to succeed Coburn. Incumbents facing reelection this year -- which includes all members of Congress -- will have to decide whether jumping in the contest is worth giving up their seats. And if they do, it would trigger more jockeying for the seats.
What was already going to be a busy year in Oklahoma politics just got busier.