Okla. Stat. tit. 20 § 3
At the regular biennial election in 1918, a justice shall be elected for each of said four additional districts, who shall be nominated by the electors of the district in which he resides, at the primary election, next preceding such biennial election. The justice for districts six and nine shall be elected for a term of six (6) years; the justice for district number seven, for a term of four (4) years, and the justice for district number eight, for a term of two (2) years, and thereafter, three of the Justices of the Supreme Court shall be elected at each general biennial election to serve for a term of six (6) years each, from the second Monday in January, succeeding his election. The successors to the existing five justices shall be elected at the time authorized by existing laws, it not being the purpose of this act to disturb the terms or districts of such justices.
Okla. Stat. tit. 20, § 3