Oklahoma constitution
Article VI: executive power
Section 15

The Lieutenant Governor shall possess the same qualifications of eligibility for office as the Governor. He shall be president of the Senate, but shall have only a casting vote therein, and also in joint vote of both houses. If, during a vacancy of the office of Governor, the Lieutenant Governor shall be impeached, displaced, resign, die or be absent from the State, or become incapable of performing the duties of the office, the president, pro tempore, of the Senate, shall act as Governor until the vacancy be filled or the disability shall cease; and if the president, pro tempore, of the Senate, for any of the above enumerated causes, shall become incapable of performing the duties pertaining to the office of Governor, the Speaker of the House of Representatives shall act as Governor until the vacancy be filled or the disability shall cease. Further provisions for succession to the office of Governor shall be prescribed by law.