Two explosions at Mexico's 275,000b/d Cadereyta refinery in Nuevo Leon state left five injured, state governor Jaime Rodriguez said.
The explosions were attributed to "an accumulation of gas," Rodriguez tweeted.
Affected workers were taken to hospital for treatment for "light injuries," he said.
Pemex did not respond to questions about how the explosions may affect operations at the refinery.
The Cadereyta refinery has a coker that allows it to turn fuel oil — of which Pemex produces a larger surplus — into higher-value distillates.
Most refiners have been trying to limit their fuel oil output, especially following the implementation of the new International Marine Organization (IMO) 2020 sulphur caps on marine fuel that took effect at the start of this year.
But Pemex's operational constraints mean that its high-sulphur fuel oil (HSFO) surplus has persisted. Pemex has coking capacity in only three of its six refineries.
