If executions set for Alabama, Texas and Florida are carried out Thursday as scheduled, it would mark the first time in more than eight years that three convicted killers were put to death in the U.S. on the same day. According to statistics kept by the Washington, D.C.-based Death Penalty Information Center, it is not uncommon for multiple executions to be scheduled in one day, but it is unusual for them all to be carried out. That's because punishments often are halted by courts and execution dates often are withdrawn or rescheduled. States have carried out three or more executions 13 times since capital punishment was reinstated in the U.S. in 1977. The most recent time was on Jan. 7, 2010, when executions took place in Louisiana, Ohio and Texas. Four prisoners were put to death Dec. 9, 1999, in Oklahoma, Indiana, Texas and Virginia. The prisoners set to die Thursday are Doyle Lee Hamm in Alabama; Thomas "Bart" Whitaker in Texas; and Eric Scott Branch in Florida. Hamm, 61, is set to die for the 1987 shooting death of an Alabama motel clerk during a robbery. Whitaker, 38, faces lethal injection for masterminding the fatal shootings of his mother and brother at their suburban Houston home in 2003. Branch, 47, is set to die for the 1993 rape and fatal beating of a college student. The number of executions in the U.S. peaked at 98 in 1999 and has trended downward since. So far in 2018, three prisoners have been executed in the U.S, all in Texas. Last year, 23 prisoners were executed in the nation, three more than the previous year.