Let's just run through the some of the possibilities.
First of all, Gov. Mary Fallin said Friday that she won't run for Senate. Not really a surprise, as she's focused on her re-election campaign, and may have her eye on something bigger.
Now for other statewide elected officials. State Auditor Gary Jones wouldn't be interested. Neither would State Superintendent Janet Barresi, or Corporation Commissioner Dana Murphy. Some have mentioned Corporation Commissioners Patrice Douglas (former mayor of Edmond) and Bob Anthony (came in third in 2004 GOP Senate primary), but I don't see either of them doing it. I also don't think that Treasurer Ken Miller or Insurance Commissioner John Doak would run.
Lieutenant Governor Todd Lamb is a sure candidate for the 2018 gubernatorial race, so he's off my list of possibilities. Labor Commissioner Mark Costello, however, is one to watch. Everyone knows that he wants to run for something bigger, but does he go now or does he, too, run for Governor in 2018?
Attorney General Scott Pruitt is probably the most likely to run of the statewide officials. He has just about everything going for him right now. He's been in the forefront of the ObamaCare battle, and fighting other issues (like the EPA). He's a staunch conservative, and is well-liked.
Turning to current members of Congress now.
Rep. Markwayne Mullin won't run; he's barely been in the House for one year, and is the most unlikely of Oklahoma's congressmen to advance to a higher level. Rep. Frank Lucas has his Ag chairmanship, and seems to be content staying in the House. He would probably struggle in building a statewide campaign, as well. Rep. Tom Cole is being mentioned, but as the moderate in Oklahoma's delegation would have a hard time winning the primary. Also, he is probably more interested in becoming chief of the Chickasaw Nation than becoming a Senator.
Rep. James Lankford will probably run. He has made meteoric strides in the House leadership (he's the fifth-highest ranked Republican in leadership), but this is an opening that he may not wish to pass up. I like Lankford. He's very genuine and personable, highly intelligent, and is a great communicator. However, some conservatives are wary of his ties to GOP establishment figures leaders like Speaker Boehner and Tom Cole.
As the former director of Falls Creek, the massive Oklahoma Southern Baptist youth camp, Lankford has the potential for a huge grassroots network across the state - something that no other candidate can probably match.
Rep. Jim Bridenstine is bound to be thinking very hard about this race. From his very first day in Congress, Bridenstine has solidly been among the most conservative Republicans in Washington, developing close associations with Senators Rand Paul and Ted Cruz, as well as other Tea Party favorites in Congress. I like Bridenstine a lot.
However, Bridenstine is not as prolific a fundraiser as many of the other names on this list, and running a statewide campaign as a freshman Congressman will pose a challenge. Additionally, you can count on the DC establishment to work hard to defeat him.
Oklahoma Speaker of the House T.W. Shannon is thought to be considering running as well, although I'm leaning to him staying in the State House. It may still be too soon for him to take on bigger names like Pruitt and Lankford and run a successful statewide campaign.
Other people that might be thinking of running could be J.C. Watts, Kirk Humphreys, Todd Hiett, or Frank Keating. Frankly, I don't think any of those decide to get in.
If I broke it down to chance of running, I guess this would be my list:
75% - Lankford
65% - Pruitt
55% - Bridenstine
35% - Costello
25% - Shannon
The rest would be in the "less than 10%" category.