Midazolam, a benzodiazepine, was developed in the 1970s and became one of the world’s most commonly used sedatives; it is used to make a prisoner unconscious and limit pain.

The debate over lethal injection, which prompted court cases, execution delays and struggles to obtain drugs, led Oklahoma in 2015 to make nitrogen gas its backup execution method in instances when lethal injection could not be used. The last inmate to be executed in Oklahoma was Charles Frederick Warner, in January 2015.

At the news conference in Oklahoma on Wednesday, officials did not discuss the use of sedatives, but said they had not yet determined a protocol in which to carry out executions with nitrogen.

Death penalty policy experts said that if a federal court approved the method, it would take at least six months — and probably longer — for such an execution to be carried out.

Robert Dunham, executive director of the Death Penalty Information Center, which opposes the death penalty, called the potential use of nitrogen in capital cases “an experimentation” that would likely cause suffering.

Oklahoma officials said they had chosen nitrogen in part because it is often used in places where assisted suicide is legal. But Mr. Dunham said that a morbidly ill person voluntarily dying with the aid of sedatives and surrounded by loved ones, and an inmate being put to death against his or her will, were hardly comparable.

“There is a significant difference between when someone is seeking to terminate their own life — and they are not struggling and are willfully participating — and what happens when you involuntarily seek to terminate the life of someone who wants to live, and who will be struggling and trying not to breathe,” Mr. Dunham said.