10 April 2015 :

The Oklahoma Senate voted 41-0 in favor of HB 1879, which legalizes execution by nitrogen hypoxia. Said by supporters to be more humane than using gases that cause suffocation, nitrogen hypoxia causes death when nitrogen gas pumped into the chamber depletes the oxygen supply in the blood.
The bill was approved by the House on March 3, and now goes to Gov. Mary Fallin (R) for signature.
Reached by The Huffington Post Thursday, a gubernatorial spokesman declined to comment on the legislation until the governor's office has reviewed the measure. Lethal injection is still the primary execution method in Oklahoma and all 31 other states that have the death penalty. The nitrogen gas chamber would be employed as a secondary method should lethal injection drugs become unavailable, or in the event the state's protocol is deemed unconstitutional when the Supreme Court examines its legality later this month.
Rep. Mike Christian (R) sponsored the bill. Oklahoma is at the center of a forthcoming Supreme Court decision for its use of the drug midazolam, which was used in the botched 2014 execution of inmate Clayton Lockett. All executions in Oklahoma have been stayed pending a ruling.