One day before Clayton Lockett was scheduled to be executed for the 1999 shooting death of 19-year-old Stephanie Nieman, a sharply divided Oklahoma Supreme Court granted a stay.
The decision also includes a second inmate, Charles Warner, who was convicted in the 1997 death of his roommate's 11-month-old daughter.
He was scheduled to die on April 29.
The two death row inmates have challenged the secrecy surrounding the source of the state's lethal injection drugs.
The decision was 5-4.
Last month, Oklahoma County District Judge Patricia Parrish struck down the state's execution law.
The ruling said the protocol prevented the inmates from seeking information about the drugs used in lethal injections and that violated their rights under the state constitution.
The state changed its execution protocol on March 21 to allow five different potential drug combinations for execution by lethal injection.
The state informed lawyers for the inmates on April 1 that the inmates would be executed using a combination of midazolam, pancuronium bromide and potassium chloride never before used in the state.
Executions have been conducted using the drug combination in Florida with lower doses.
The request filed by the convicts attorney says the inmates "have received no certifications, testing data, medical opinions or other evidence to support the state's insistence that these drugs are safe, or to prove that they were acquired legally."
Oklahoma and other states that have the death penalty have been scrambling for substitute drugs or new sources for drugs for lethal injections after major drug companies — many based in Europe with longtime opposition to the death penalty — stopped selling to prisons and corrections departments.
On Friday, the Oklahoma Court of Criminal Appeals denied the inmates' request for a stay in spite of a ruling by the Supreme Court earlier in the week that the appeals court had the authority