A number of US states may revert to killing their death row inmates with electric chairs, firing squads and gas chambers as it becomes increasingly difficult to buy the chemicals used for lethal injections.
The European Union has banned the export of one of the most common sedatives used in lethal injections, forcing US states to experiment with new "cocktails" of drugs for executions.
One such experimental recipe was used in the botched execution of a prisoner in Oklahoma this week, leaving him writhing in pain to die of a massive heart attack 43 minutes later.
Lawyers are seeking a moratorium on executions.
The shortage of execution drugs, together with fears the courts may intervene to ban experimental methods of lethal injection, have prompted states to look at alternative ways to kill prisoners.
Tennessee's legislature has passed a Bill that would reintroduce the electric chair if the state was unable to find drugs for lethal injections.
The state's Republican governor is still weighing whether to sign it into law.
Missouri is considering a proposal to reintroduce firing squads and gas chambers if it becomes impossible to carry out a lethal injection.
Clayton Lockett died from a heart attack after a botched execution in Oklahoma earlier this week. Photo / AP
Richard Dieter, the executive director of the Death Penalty Information Centre, said the laws were intended as symbols by conservative politicians of their commitment to the death penalty.
"It's about being even more blatant than the anti-death penalty side.
"To see this as a rational process is to miss the harshly divisive political atmosphere that produces these things," he said.
Lethal injections were adopted by US states as a painless way to put inmates to death, first with a three-drug mixture, then often with a single dose of a powerful barbiturate. It was used first on a Texas inmate in 1982.
Since 1976, 1,203 executions have been performed by injection. They are the primary execution method for all 32 US states which still have the death penalty. However, more than a dozen states also have laws that theoretically allow for gassing, hanging, electrocuting or shooting.
The use of such methods is not unheard of in the recent past. In 2013, Robert Gleason, a convicted murderer, chose to die by electric chair in Virginia.
Ronnie Lee Gardner was the last American to be killed by firing squad. He was shot in Utah in 2010 by five unnamed police officers armed with Winchester rifles.
A firing squad execution chamber. Photo / AP
Mary Fallin, the governor of Oklahoma, said the state would execute a second inmate as soon as a review of Tuesday's killing was complete.
"His fellow Oklahomans have sentenced him to death, and we expect that sentence to be carried out as required by law," Mrs Fallin said.
Texas also said the prolonged death in Oklahoma would not deter it from executing a man convicted of kidnapping a woman, raping her and then shooting her in the back as she fled from him. The execution is due to be held on May 13.
Mr Dieter said the botched Oklahoma execution was unlikely to give new momentum to campaigners seeking to abolish the death penalty but might put pressure on US states to be more transparent about where lethal drugs are being bought.
About 55 per cent of Americans support the death penalty, down from 78 per cent in 1996, while 37 per cent are opposed. President Barack Obama has said he supports the death penalty for "extraordinarily heinous crimes" such as terrorism or child murder.