Justices with the 1st District Court of Appeal were considering whether to uphold a ban on executions ordered by a Marin County judge who ruled the state had failed to comply with administrative rules in revising procedures for injecting a three-drug cocktail, the San Jose Mercury News reported Tuesday.
The highly technical rules have prevented California from conducting executions for more than seven years.
"The amount of conceded mistakes here is unusual," Justice J. Anthony Kline told Deputy Attorney General Michael Quinn.
Justices James Lambden and James Richman asked no questions during the hearing.
If the justices overturn the ban, the three-drug method could continue and could prompt resolutions of federal court challenges to lethal injection. Upholding the ban would add further delays in executing the 734 inmates on death row.
The panel has 90 days to hand down a ruling.