Lawyers for four Oklahoma inmates who are scheduled for lethal injection this winter filed an emergency request for a delay with a federal appeals court on Friday, claiming that a sedative the state plans to use cannot reliably induce the deep coma needed for a humane execution and that its use “constitutes human experimentation.”

If no stay is granted, the execution set for Thursday of one of the inmates, Charles F. Warner, will be the state’s first since the bungled killing last April of Clayton D. Lockett, who gasped and struggled against his restraints before dying 43 minutes into the procedure.

Mr. Warner had been scheduled to die the same night, but after the Lockett episode, the state temporarily halted executions in order to improve training and procedures. Mr. Warner was condemned for the rape and murder of an 11-month-old girl in 1997.

A state inquiry determined that in Mr. Lockett’s case, a doctor failed to properly insert an intravenous needle through the prisoner’s groin, causing the sedative, and then the paralytic and heart-stopping agents, to diffuse in surrounding tissue. Officials have developed new procedures that they say will prevent such an error. But they also decided to double the dose of the same sedative, midazolam, in future executions.