OKLAHOMA CITY (AP) — Oklahoma has missed a self-imposed deadline to finish creating a new execution protocol involving nitrogen gas, and it’s unclear when executions will resume in the state.

Attorney General Mike Hunter and Department of Corrections Director Joe Allbaugh announced in March that they intended to switch to nitrogen hypoxia for executions in Oklahoma. The announcement came after the state had trouble obtaining lethal injection drugs amid opposition from drugmakers to having their products used in executions.

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Officials had hoped to have the new plan drafted by July. But Hunter’s office and the Corrections Department now say there is no estimated completion date for the new protocol.

Executions have been on hold in Oklahoma since 2015 following several mishaps, including a botched lethal injection in 2014 that left an inmate writhing on the gurney and drug mix-ups in 2015 in which the wrong lethal drugs were delivered.

The department is working to ensure the protocol is “effective and humane,” said Matt Elliott, a corrections spokesman.

“It’s really just about getting it right,” added Alex Gerszewski, a spokesman for the Attorney General’s Office. “It’s important to get it right.”

The state is under court order not to perform any executions until a new execution protocol is in place, said Robert Dunham, the executive director of the Death Penalty Information Center.

Dunham said state officials are likely grappling with a number of concerns about how to obtain the odorless and tasteless gas, how to administer it to inmates, and how to protect guards and other bystanders,.

State records show 16 inmates have exhausted all appeals and are awaiting execution dates in Oklahoma.