OKLAHOMA CITY (AP) — After trying unsuccessfully for months to obtain lethal injection drugs, Oklahoma officials said Wednesday they plan to use nitrogen gas to execute inmates once the state resumes using the death penalty, marking the first time a U.S. state would use the gas to carry out capital punishment.

State Attorney General Mike Hunter and Department of Corrections Director Joe Allbaugh jointly announced the plan, saying the two agencies would work together to develop new protocols over the next several months.

Oklahoma and other states haven't been able to get the drugs required...