Executions in the state have been on hold since 2015 due to a series of problems with lethal injection drugs, including a particularly disturbing 2014 case in which an inmate "began to twitch and gasp" after the drug was administered, ultimately dying from a heart attack.
Gov. Mary Fallin in 2015 signed a measure adding nitrogen gas to the list of execution methods.
The state plans to implement a 2015 law that allows executions using nitrogen hypoxia if lethal injection is declared unconstitutional or the drugs needed to put inmates to death are unavailable, Oklahoma Attorney General Mike Hunter said.
Oklahoma's prisons chief said the readily-available gas was a better option than trying to find new lethal, injectable drugs.
Grand jurors said nitrogen gas would be easy and low-priced to obtain for executions, simple to administer and, according to scientific research, quick and seemingly painless.
As the drugs become increasing hard to obtain, Oklahoma will stop using lethal injection and plans to become the first to execute inmates using the untried method of inert gases, officials announced Wednesday.
In 2014, Oklahoma drew intense scrutiny for its death-penalty procedures after the execution of Clayton Lockett gained worldwide attention.
"It is a common procedure in states and in countries that allow for assisted suicide", Hunter said. Oklahoma would be the first state to employ the method. He said state leaders had to "to utilize an effective and humane manner that satisfies both the Constitution and the court system". "It will be some time, I think, before an execution can be scheduled". But in recent years, even those states dedicated to continuing the practice have run into roadblocks amid a shortage of lethal injection chemicals, driven in part by drugmakers' objections to the death penalty. A bill that would make the electric chair the state's default execution method is now before the House Committee on the Judiciary.
Experts have said they know of no examples of states using nitrogen gas for executions. It was not likely until the end of the year at the earliest, The Oklahoman newspaper reported.
Once the protocol is developed, the state must resolve a federal stay on executions before putting it into practice, which could take another five months or more.