Oklahoma adopted a new backup method of execution Friday, making nitrogen gas the way it will execute inmates if lethal injection cannot be utilized.

Gov. Mary Fallin (R) signed the law Friday, less than two weeks before the U.S. Supreme Court is set to hear a case challenging the way lethal injections are carried out in Oklahoma.

This change makes Oklahoma the third state over the last year to substantially alter its methods of execution amid an ongoing shortage of lethal injection drugs. However, the two other states to change their execution protocols expanded the use of backup options that were already in place: Utah made firing squads the default alternative last month, while Tennessee did the same thing with the electric chair; both methods had been available for some inmates, depending on when they were sentenced.

As the drug shortage has persisted in recent years, states with capital punishment have considered reviving older methods, but most of these suggestions have gone nowhere. Unlike the laws in Utah and Tennessee, the new Oklahoma law is the first time a state has added a method that was not already on the books.

In Oklahoma, current law states that if lethal injection is deemed unconstitutional or is just not available, the electric chair is the backup option, while the firing squad is the third option. The new law makes nitrogen hypoxia the backup method, with the electric chair and firing squad serving as the third and fourth options, respectively.

One of the state legislators who sponsored the Oklahoma bill said that the new method would involve an inmate breathing in just nitrogen without oxygen, which he said would lead to the inmate becoming unconscious within 10 seconds and dead within minutes. While the bill itself offers few details regarding how such executions would be carried out, a financial analysis prepared for the state representatives described the process as requiring only a gas mask and a container of nitrogen.

“The costs would be minimal and include the one time purchase of a gas mask (similar to what one experiences at the dentist), and the price for a canister of nitrogen,” the financial analysis said.

This analysis noted that it “would be relatively cost effective” and could save the Department of Corrections money. It went on to estimate that it costs the state about $500 for each execution currently, though it added that “it is impossible” to come up with a precise figure due to the secrecy laws governing executions in the state.

“Oklahoma executes murderers whose crimes are especially heinous,” Fallin said in a statement after signing the bill. “I support that policy, and I believe capital punishment must be performed effectively and without cruelty. The bill I signed today gives the state of Oklahoma another death penalty option that meets that standard.”

It is not clear if nitrogen gas has been used as a formal method of execution before, but there do not appear to be any cases. Adopting a new method is not new for Oklahoma, which became the first state in the country to make lethal injection a method of execution in 1977. (It was not the first state to carry out such an execution, though, as Texas used it for the first time five years later.)

While proponents of the bill described it as humane, Robert Dunham, executive director of the Death Penalty Information Center, said the same idea — “the myth [of a] quick, painless and effective” execution — was used to sell lethal injection.

“I think that Oklahoma has acted first and thought second in the manner it’s gone about conducting executions,” he said Friday. “And the hasty manner in which this bill sped into law reflects the same lack of care with which Oklahoma has managed its execution process historically.”

Lethal injection remains the primary method of execution for every state that has the death penalty as well as the federal government. A handful of states have other methods available including electrocution, the gas chamber and the firing squad, with the electric chair being the most common alternative. In Virginia, for example, inmates are allowed to select the electric chair over lethal injection, something that last happened in 2013.

The Oklahoma Department of Corrections said Friday it did not have a protocol in place to carry out executions through the new method approved Friday.

“We would come up with a protocol, but we have not done so,” said Terri Watkins, a spokeswoman for the department. Watkins said the department also does not have any protocols in place for the electric chair or firing squad, the state’s current backups.

“We plan to maintain our current protocol of lethal injection,” Watkins said.

She said she could not answer other questions about what the department plans to do if the Supreme Court strikes down its lethal injection procedures because there is pending litigation.

The nitrogen hypoxia bill in Oklahoma overwhelmingly passed the state’s House of Representatives in March and the state Senate earlier this month. It goes into effect in November.

“With the current method of executions under attack and judicial scrutiny, it is imperative that we find an alternate way of delivering justice,” state Rep. Mike Christian, a Republican who represents Oklahoma City and sponsored the House bill, said in a statement earlier this month.

Supporters of the legislation said that it gives the state a way forward if its current lethal injection protocols are struck down by the Supreme Court. Christian called nitrogen hypoxia “practical, efficient and humane” in a separate statement. He also said that unlike lethal injection, which relies upon drugs that can be hard to find, this method would not have the same issues.

“There is no way for death penalty opponents to restrict its supply,” he said.

The ongoing shortage of lethal injection drugs has fractured the execution landscape in the United States. Fewer states are sentencing inmates to death and carrying out executions, but for the ones that still plan to put inmates to death, the lack of drugs has caused experimentation and a certain amount of chaos.

Texas, the country’s leading death-penalty state, was on the verge of running out of drugs recently before it obtained enough to carry out its next few executions. It could run out again before executions scheduled for May and June, and it is unclear what officials there will do if they cannot find more drugs.

This drug shortage is why Oklahoma had to change the execution drugs it used, adopting a new protocol that the state used for the first time in the botched execution of Clayton Lockett last year. Lockett, who was convicted of murder, kicked, bucked his body and grimaced during his execution, ultimately dying 43 minutes after it began.

After Lockett’s execution went awry, drawing criticism from the White House and United Nations, Oklahoma halted executions and Fallin ordered an investigation. This inquiry said that the execution team failed to properly place the IV and had no idea what to do when problems emerged.

There were also issues last year with executions in Ohio and Arizona, which — like the Oklahoma execution — involved midazolam, a sedative. The inmate in Arizona gasped and snorted for nearly two hours before dying. Ohio said earlier this year it was no longer using midazolam and delayed all of the executions it had scheduled for this year while it sets up a different lethal injection protocol.

Oklahoma adopted a new lethal injection policy last fall that kept the same three drugs it used during Lockett’s execution, but it ratcheted up the dose of midazolam. Oklahoma’s lethal injection policy now includes 500 milligrams of midazolam, five times as much as it meant to use on Lockett and the same amount used by Florida (which has used midazolam in executions since 2013).

In January, Oklahoma carried out its first execution since the botch, using the new lethal injection policy to put Charles Warner to death. Warner, who was convicted of raping and murdering an 11-month old, was scheduled to be executed the same night as Lockett, but his execution was delayed for more than eight months.

The U.S. Supreme Court declined to stay his execution, but Justice Sonia Sotomayor wrote a dissent that specifically questioned whether midazolam could really “work as intended…given recent experience with the use of this drug.” Sotomayor was joined by the court’s three other liberal justices in saying she would have halted the execution, but because it takes five justices to issue a stay, the execution proceeded.

It takes only four justices to accept a case, rather than five, and the Supreme Court said the following week that it would hear a case from inmates challenging Oklahoma’s lethal injection protocol. Arguments are set for the end of the month, with a decision expected in June.

Until the justices announce their decision, executions have been halted in Oklahoma, Florida and Alabama. Tennessee said this week it was canceling its scheduled executions due to other court challenges.