MEXICO CITY, May 2 (Reuters) - The former head of

Mexican state oil firm Pemex's exploration and production arm

has returned to his post after the surprise departure of the

previous chief earlier this week, three sources told Reuters on

Friday.

Petroleum engineer Angel Cid Munguia had served as the head

of Pemex Exploration and Production through the administration

of President Andres Manuel Lopez Obrador, but was replaced by

Nestor Martinez when President Claudia Sheinbaum took office in

October.

Three sources with knowledge of the matter told Reuters

that Martinez had stepped down on Wednesday. Two of them said

that Cid Munguia's return to his former post was immediate.

Neither Pemex nor the Energy Ministry responded to

Reuters requests for comment.

Two of the sources said that Cid Munguia had been acting

as adviser to Energy Minister Luz Elena Gonzalez before his

return. Three sources said that Martinez, once a commissioner at

the now-defunct oil regulator CNH, would stay at Pemex as an

adviser to CEO Victor Rodriguez.