Richard Glossip's execution was delayed on Wednesday after officials discovered they did not have the correct drugs to perform the procedure.
Oklahoma Attorney General Scott Pruitt had requested the freeze on executions to give the state time to investigate.
The Oklahoma's highest criminal court agreed on Friday.
In addition to Glossip, the executions of inmates Benjamin Cole and John Grant have also been indefinitely delayed.
State prison officials said they were posted potassium acetate instead of potassium chloride, the third drug used in Oklahoma's lethal injection formula.
The court ordered the state to provide status reports every 30 days.
Executions have been delayed recently in the US amid problems buying drugs as many firms have refused to sell them.
The state has overhauled how it carries out the death penalty after the botched execution of Clayton Lockett in 2014. Lockett struggled and took more than 40 minutes to die.
Typically, inmates become sedated and are declared dead within minutes.
Glossip's boss Barry Van Treese, the owner of the Oklahoma City motel, was beaten to death in 1997.
His colleague Justin Sneed was convicted of the killing but said Glossip had ordered him to carry it out.
Glossip and his family have maintained his innocence for nearly 20 years, saying that Sneed acted alone.
He was first convicted in 1998 but that was overturned in 2001, only for Glossip to be convicted again three years later.
In the most recent appeals, his lawyers said they had an affidavit from another inmate who said Sneed admitted to setting Glossip up.
British billionaire Richard Branson took out a full-page ad in The Oklahoman newspaper on Wednesday that argued Glossip is innocent.
Pope Francis had urged Oklahoma Governor Mary Fallin to halt Glossip's execution. Ms Fallin said she did not have the authority to do so.

In November, the Chancellor scrapped planned major cuts in police funding, announcing budgets would be protected in real terms, as long as council tax precepts were raised.
Seventy extra officers will now be recruited.
Police Commissioner John Dwyer said a public consultation supported the rise.
The force had expected £30m of budget cuts over the next four years but - as long as council tax also rises in future years - is now forecasting a funding increase of £1.1m by 2020.
Mr Dwyer said the new budget would "ensure the constabulary had the resources necessary to protect the people of Cheshire".
The number of police officers in the county will now increase to 2,053.
Residents in Band D properties will see taxes rise by £5 from April, meaning the portion of the bill payable to the police will be £161.23.
The force's council tax precept has increased in two of the past four years.
Three impending executions in Oklahoma have been halted after prison officials nearly administered the wrong lethal injection drug to a death row inmate.
[NEXT_CONCEPT]
Cheshire Police is to raise its share of council tax by 3.2%, after the government announced a 1.4% cut to police funding.