In more than half of the U.S., lethal injections are the preferred method of execution, according to the Death Penalty Information Center. Other methods include lethal gas, electrocution, firing squad or hanging.
Connecticut, New Mexico and Maryland have abolished the death penalty, but those inmates on death row before abolition with be executed by injection. In Maryland, there is a potential for execution by lethal gas.
Here's a closer look at executions methods by state, according to data from the Death Penalty Information Center.
Here's a closer look at where executions have occurred since 1976 from the Pew Research Center.
Source: Pew Research Center