By Adriana Barrera

MEXICO CITY, Dec 18 (Reuters) - Mexico's state oil company Pemex is preparing to replace the head of its exploration and production arm, just months after he returned ​to the post, three sources familiar with the matter told Reuters, as the company struggles ‌to stem a decline in crude output.

Angel Cid Munguía resumed leadership of Pemex Exploration and Production (PEP) in early May. He previously ‌held the role until the end of former President Andres Manuel Lopez Obrador's term, which ended when President Claudia Sheinbaum took office last October.

The change at the helm of PEP would be the third under Sheinbaum, who has pledged to keep national oil output averaging 1.8 million barrels per day through the end ⁠of her term in 2030. That ‌target looks increasingly difficult as mature fields decline, new discoveries fall short and offshore projects Zama and Trion, which Pemex is developing with partners, move slowly.

Two of ‍the sources said Cid is expected to be succeeded by Octavio Barrera Torres, an electronics engineer appointed in May as deputy director of design, engineering and project execution at PEP as part of a company restructuring.

"It seems he ​didn't deliver on promises to boost production," one source said of Cid, who had served as ‌an adviser to Energy Minister Luz Elena Gonzalez before returning to Pemex.

Pemex did not immediately respond to a request for comment on Cid's possible departure, which would come after the signing of the first mixed contracts, a new partnership scheme with private firms aimed at lifting oil and gas output.

The program has so far drawn little interest from the industry, hampered by Pemex's heavy debt load.

Cid and Torres did ⁠not immediately respond to Reuters emails seeking comment on the ​leadership change at PEP.

Reuters reported this week that Pemex had ​awarded five of the 11 mixed contracts it aimed to finalize before year-end, deals it estimated could add nearly 70,000 barrels per day (bpd) to current output of 1.6 ‍million bpd, including partners. The ⁠awards have faced repeated delays.

Pemex also faces more than $100 billion in financial debt despite multibillion-dollar capital injections and tax breaks from the government.

Between January and September, the company received around 380 ⁠billion pesos ($21.13 billion) in government contributions, an increase of more than 150% from the same period last year, according to ‌Pemex data.

($1 = 17.9821 Mexican pesos)

(Reporting by Adriana Berrera; Writing by Adriana Berrera and Sarah ‌Kinosian; Editing by Ana Isabel Martinez and Chizu Nomiyama )