On April 15, filing for the Oklahoma primary for Congress, state office, and partisan county office, closed. Here is a link to the candidate list.
Thirteen Libertarians filed for legislature. Assuming none of them withdraws, this will be the highest number of minor party legislative candidates in Oklahoma since 1936 or 1934. The Libertarian Party is the only party on the ballot, other than the Republican and Democratic Parties. Other years in which the Libertarians had party status in Oklahoma are 1980, 1984, 1996, and 2000.
The number of Libertarians running for the legislature in past years has been: 1980 three; 1984 twelve; 1996 one; 2000 five. In 1984 Libertarians were permitted to nominate by convention, so it was somewhat easier than normal for candidates to come forth.
The number of Reform Party legislative candidates was: 1996 one, 1998 one, 2000 zero.
The number of American Party legislative candidates was: 1968 zero, 1970 one, 1972 two.
Before the American Party, the last third party on in Oklahoma was Prohibition, which had the following number: 1934 zero, 1936 three, 1938 five, 1940 two, 1942 one, 1944 zero.
The Socialist Party was last on in 1936 and 1934. The number of legislative candidates it had those years is unknown, but it is very likely that in 1934 at least it was higher than thirteen.