OKSB Southwest Bancorp, Inc.

Southwest Bancorp, Inc. 2008 Stock Based Award Plan

Southwest Bancorp, Inc. 1999 Option Plan

(Full title of the plans)

c/o George A. Makris, Jr.

Chairman and Chief Executive Officer

c/o Simmons First National Corporation

501 Main Street

Pine Bluff, Arkansas 71601

(870) 541-1000

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies of all communications should be sent to:

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act:

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

DEREGISTRATION OF SECURITIES

These post-effective amendments relate to the following Registration Statements on Form S-8 (together, the “ Registration Statements ”) of Southwest Bancorp, Inc. (the “ Company ”) filed by the Company with the U.S. Securities and Exchange Commission (the “ Commission ”):

Pursuant to the Agreement and Plan of Merger, dated as of December 14, 2016, as amended by Amendment No. 1 to the Agreement and Plan of Merger, dated as of July 19, 2017 (as amended, the “ Merger Agreement ”), by and among the Company and Simmons First National Corporation (“ Simmons First ”), on October 19, 2017 the Company merged with and into the Simmons First, with Simmons First surviving the merger (the “ Merger ”). Pursuant to the terms of the Merger Agreement, the Shares issued and outstanding immediately prior to the effective time of the Merger (other than Shares to be cancelled in accordance with the Merger Agreement) were cancelled and converted into the right to receive 0.3903 shares of Simmons First common stock and $5.11 in cash per Share.

As a result of the consummation of the Merger, the Company has terminated all offerings of the Shares pursuant to the Registration Statements. In accordance with an undertaking made by the Company in each of the Registration Statements to remove from registration, by means of a post-effective amendment, any securities that remain unsold at the termination of the offering, the Company hereby removes from registration any and all Shares registered under the Registration Statements that remain unsold as of the date hereof.