Oklahoma will start using inert gas or nitrogen to complete state-sponsored executions, officials announced Wednesday, making it the first state to use the gas for that purpose.

Executions have been on hold in Oklahoma due to problems with the lethal injection method, but with the new method of performing executions announced, they will resume for the first time in more than three years.

The Hill reports: The state attorney general, Mike Hunter (R), and corrections director, Joe Allbaugh, said during a news conference that the gas will become Oklahoma’s primary method of execution after a protocol is finalized, according to local ABC affiliate KOCO.

The report continues: The introduction of nitrogen comes as the state has had difficulties obtaining the proper substances for lethal injections, the state attorney general’s office said.

A 2015 state law allows the use of nitrogen, which depletes the body of air, for executions if the proper lethal drugs are unavailable or ruled unconstitutional. The next year, a grand jury recommended nitrogen for official use, citing its reportedly quick and humane effect. 

The Oklahoman reported that the gas could be used by the end of the year.