Texas prison officials have acquired a small supply of pentobarbital to replenish their dwindling inventory of the execution drug so lethal injections set for next month in the nation's most active death penalty state can be carried out, the Texas Department of Criminal Justice said Wednesday.

Four prisoners already have been put to death this year in Texas. That left enough pentobarbital in the state's inventory to conduct only one more lethal injection, the scheduled April 9 execution of Kent William Sprouse, convicted of the shooting deaths of a North Texas police officer and another man in 2002. Sprouse is the first of four Texas inmates set to die in April.

The agency now has a sufficient amount of the powerful sedative for the other three, spokesman Jason Clark confirmed. At least two more prisoners face punishment in May and June and would require yet another drug acquisition.

Pharmaceutical companies, under pressure from death penalty opponents, have stopped selling U.S. prisons drugs for lethal injections. So Texas and other states have turned to less regulated compounding pharmacies for made-to-order drugs. States also are exploring other methods of execution.

As in the past, Texas prison officials Wednesday refused to identify the provider of the new supply.

Officials have insisted the drug supplier's identity should remain secret to keep the provider from harm and threats of retaliation.

Clark would confirm only that the new drugs were purchased "from a licensed pharmacy that has the ability to compound." He declined to say if it was the same provider the agency has used previously.

"We continue to explore all options including the continued used of pentobarbital or alternate drugs to use in the lethal injection process," he said.

Texas prison officials could change the drug used for executions but Texas lawmakers would have to enact any change of method. No measures to do so have been proposed, although two identical bills in the Texas Senate and House would allow the identity of execution drug suppliers to remain confidential.

A state judge last year ordered the Department of Criminal Justice to divulge the source. That ruling is on hold pending the outcome of an appeal by the Texas Attorney General's Office. An appeals court this week granted the state's request and put off until late next month the deadline for the state to file its arguments in the case.

The use and availability of drugs for executions has come under heightened scrutiny after lethal injections last year went awry in Oklahoma, Arizona and Ohio.

This week, Utah's governor signed a law allowing that state to use firing squads if drugs for lethal injection can't be acquired. In Oklahoma, where the state's injection method is under review, lawmakers gave preliminary approval to a measure that would allow use of nitrogen gas for executions if drugs for lethal injection were not available.

An execution earlier this month in Georgia was put off when prison authorities questioned the appearance of the compounded pentobarbital they planned to use.

Texas has executed a nation-leading 522 inmates since 1982, when it became the first state to use lethal injection.