A shortage of the lethal chemicals needed to execute prisoners has some states with pending executions considering new methods of killing condemned prisoners — including ones that haven’t been used for more than half a century.

Lawmakers in several states have proposed bills this year to allow executions by firing squad, gas chamber and electrocution, if the chemicals necessary for lethal injections are unavailable.

The shortage stems from the European drug manufacturers who produce ingredients for the lethal three-drug cocktail that most states use. The European Union, which opposes the death penalty, had threatened to limit exports of one drug if it was to be used in executions; the drug, propofol is a common anesthetic used in hospitals.

In 2012, the Food and Drug Administration asked several states to turn over their foreign-made lethal injection drugs, to comply with a court order.

Many states moved away from methods of execution like the electric chair and gas chambers in the 1980s, toward what death penalty supporters said was a more humane way of taking a life. Lethal injections typically followed a three-step process using drugs that would render a recipient unconscious, cause paralysis and finally stop the heart.

Now that supplies are running short, several states have changed their formulas. Last month, Ohio executed a prisoner using a two-drug cocktail that included a sedative and a high-powered painkiller. Louisiana, which is scheduled to execute a convicted murderer next week, plans to use the same recipe.

Other states are looking to different options. Missouri state Rep. Rick Brattin (R) has proposed a measure that would make firing squads an option if lethal injection is unavailable, the Associated Press reported Wednesday. A similar bill has been introduced in Wyoming, while the Virginia legislature could take up a bill that would allow death by electrocution.

Last year, Missouri Gov. Jay Nixon (D) issued a stay of the execution of a convicted serial killer scheduled to die in October due to the shortage. The state Department of Corrections switched to a different drug, and the killer was executed in November. On Wednesday, Missouri executed a man for a 1991 murder, though the state wouldn’t disclose where it obtained the drugs used in the execution.

Thirty five states, along with the U.S. government and the U.S. military, authorize executions by lethal injections. Eight states use one lethal dose of an anesthetic to execute prisoners, according to the Death Penalty Information Center.

Eight states allow the death penalty by electrocution, and three use the gas chamber. Three states allow prisoners to be hanged, while the firing squad is still an option in two states, Utah and Oklahoma. In all states that allow the death penalty, lethal injection is the primary method of execution; most states with alternative options only allow prisoners who committed crimes before a certain date to choose those methods of execution.

Since the death penalty was reinstated by the Supreme Court in 1976, states have executed 1,364 prisoners. Those numbers peaked in 1999, when 98 people were put to death, but the number of executions has fallen off significantly in recent years. Forty-three people were executed in both 2011 and 2012, and 39 people were executed in 2013, the DPIC reported.

As of April 1, 2013, 3,108 inmates sat on death row, according to a report produced by the NAACP Legal Defense and Education Fund. About 1,341, or 43.1 percent, are white, while 1,300, 41.8 percent, are African American, the NAACP’s survey found.