TULSA, Oklahoma - Oklahoma House Speaker T.W. Shannon formally entered the GOP race for the open U.S. Senate seat in Oklahoma, while Republican U.S. Representative Jim Bridenstine said he won't be running for the position.

Shannon (R-Lawton) announced his intention to run during a news conference at the Tulsa Historical Society Wednesday morning.

Meanwhile, Bridenstine said Wednesday he wouldn't run for the Senate seat left open by Senator Tom Coburn's resignation. The first-term congressman made his announcement moments before Shannon formally declared his candidacy.

"Since Dr. Tom Coburn's retirement announcement, I have been honored and overwhelmed by encouragement to succeed him as Oklahoma's senator.

After giving this matter serious consideration and prayer, my family and I have decided I will not to run in the special election to complete Dr. Coburn's term.

I would like to thank my faithful supporters who have provided so much encouragement. Their extraordinary outpouring of support strengthens my resolve to continue our efforts in the U.S. House of Representatives."

Shannon will join two-term Congressman James Lankford in the race for the Republican nomination.

A Democrat hasn't been elected to an open U.S. Senate seat in Oklahoma since David Boren in 1978, and Republicans are heavily favored to maintain it. No Democrats have formally announced intention to run.

The Associated Press contributed to this report.