Only two states saw a smaller share of eligible voters cast ballots in 2012, and just seven states had a smaller share of residents registered to vote, according to census data. ... It's a rough assessment... Oklahoma scores higher than any other state on political disengagement -- ahead of Arkansas, Arizona, Tennessee and Texas.FairVote recently reported on the subject of Oklahoma voter turnout in presidential elections. In 1992, Oklahoma's voter turnout was above the nationwide turnout. However, as the state's underlying partisanship has become more safely Republican, the state's turnout has declined, falling below the nationwide voter turnout in every election since 1996.
The possible reason is that presidential campaigns have little incentive to pay attention to the safe state of Oklahoma. In 2004, 2008, and 2012, neither major party held a campaign event in Oklahoma after the party conventions. Additionally, (as the Washington Post article quotes FairVote reporting), in the 2012 presidential elections, the two major candidates spent a total of $1,300 on campaign ads in the state.
Ultimately, the current Electoral College rules are to blame. Most states allocate their electoral votes using a winner-take-all system, incentivizing candidates to devote all of their attention to swing states and to ignore safe states. This leaves states like Oklahoma on the sidelines and their voters without voices in presidential elections.
For more analysis, read FairVote's blog post, "Oklahoma Voter Turnout Suffers without National Popular Vote Plan."