On Wednesday night, the Supreme Court stopped an execution by lethal injection. The condemned Missouri man, Russell Bucklew, says he has a medical condition, affecting his veins, that would make the injection cause hemorrhaging—and make him feel like he’s choking on his own blood. The court took the unusual step of intervening at the last minutes, when every other court had turned Bucklew down, and also of sending the case back to the lower courts to decide whether to hold a hearing about Bucklew’s claim.

The Supreme Court ruled in 2008 that Kentucky’s three-drug protocol for carrying out lethal injections was constitutional, but there’s no question that the method looks grimly suspect in the wake of Clayton Lockett’s apparently painful, botched execution in Oklahoma last month. Not so long ago, though, this was the method that represented progress. Hanging. Firing squad. The guillotine. The electric chair. The gas chamber. Lethal injection. Every age seems to feature a new and improved method of capital punishment, billed as more efficient and humane. The spectacle of Lockett’s death, and the Supreme Court’s hesitation, shines a spotlight on the latest idea—death by nitrogen.

This new proposed method, known as nitrogen asphyxiation, seals the condemned in an airtight chamber pumped full of nitrogen gas, causing death by a lack of oxygen. Nitrogen gas has yet to be put to the test as a method of capital punishment—no country currently uses it for state-sanctioned executions. But people do die accidentally of nitrogen asphyxiation, and usually never know what hit them. (It’s even possible that death by nitrogen gas is mildly euphoric. Deep-sea divers exposed to an excess of nitrogen develop a narcosis, colorfully known as “raptures of the deep,” similar to drunkenness or nitrous oxide inhalation.)

You can oppose the death penalty and still see the merit in making executions more humane. As Boer Deng and Dahlia Lithwick argued in Slate, opponents of the death penalty inadvertently have made lethal injection less safe, by forcing prison officials into using inferior methods and substandard drug providers. As the states struggle to obtain drugs, such as pentobarbital, for lethal injections because of an export ban by the European Union, lethal injection has been turned from a method of execution into a medical experiment.

Proponents say that death by nitrogen, by contrast, adheres to the constitutional prohibition against cruel and unusual punishment. The condemned prisoner would detect no abnormal sensation breathing the odorless, tasteless gas, and would not undergo the painful experience of suffocation, which is caused by a buildup of carbon dioxide in the bloodstream, not by lack of oxygen.

In late April, Louisiana Department of Corrections Secretary James LeBlanc suggested to a state legislative committee that Louisiana should look into using nitrogen gas as a new method of execution, since lethal injection has become so contentious. “It’s become almost impossible to execute someone,” LeBlanc complained to the Louisiana House Administration of Criminal Justice Committee.

“Nitrogen is the big thing,” LeBlanc told the committee. “It’s a painless way to go. But more time needs to be spent [studying] that.” The committee instructed LeBlanc to do some research on the subject and report back. In the meantime, Louisiana has delayed a pending execution. “I’m not taking anything off the table,” says state Rep. Joseph P. Lopinto III, chairman of the state’s Administration of Criminal Justice Committee. “If someone says nitrogen gas is the way to go, then we can debate that and do it if need be.”

As long as 32 states have capital punishment on the books, there should be a less reliably cruel method of execution than lethal injection. “If we’re going to take a life, then we should do it in the most humane, civilized manner as is possible,” says Lawrence Gist II, an attorney and professor of business and law at Mount St. Mary’s College. “Right now, nitrogen is the best of the available options.”

Gist, a death penalty opponent, runs a website dedicated to promoting nitrogen asphyxiation for state-sanctioned executions. Polling suggests the public could get behind the idea. In a recent NBC News poll, 1 in 3 people said that if lethal injections are no longer viable, executions should be stopped altogether. But many others were open to alternative methods of putting prisoners to death. About 20 percent opted for the old version of the gas chamber (which traditionally used hydrogen cyanide to kill), 18 percent for the electric chair, 12 percent for death by firing squad, and 8 percent for hanging.

Nitrogen gas, unlike the lethal drugs that states have relied on, is widely available. The gas is used extensively in industrial settings, from aerospace to oil and gas production “Lethal injection is just fine if you can get the pentobarbital,” says Kent Scheidegger, legal director of the Criminal Justice Legal Foundation, a group that favors capital punishment. “But if that’s not available, an alternative like nitrogen gas would work.”

In contrast to lethal injection, no medical expertise would be needed to introduce nitrogen gas into a sealed chamber. The gas chamber itself is technology that has been around since the 1920s. In fact, three states—Arizona, Missouri, and Wyoming—still authorize lethal gas as a method of execution (depending on the choice of the inmate, the date of the execution or sentence or the possibility that lethal injection is held unconstitutional).

The last gas chamber execution in the U.S. was in 1999—the method fell out of favor because hydrogen cyanide is a poison causing suffering that lasts 10 minutes or longer. Lethal injection, of course, was supposed to be painless and better. What if it’s not? That’s the question the Supreme Court now finally seems to be returning to. The history of capital punishment suggests that as long as there’s a will to kill criminals, someone will come up with an improved way. The new tool in the executioner’s bag may turn out to be nitrogen, a better way to carry out a gruesome task.