MOSCOW, Nov 13 (Reuters) - Kazakhstan's biggest oil

field Tengiz, operated by U.S. major Chevron ( CVX ), has

reduced oil output by around 21% on average since Oct. 26 to

62,600 metric tons per day, or 496,200 barrels per day, three

industry sources told Reuters on Wednesday.

The Central Asian nation, which relies on Tengiz and two

other major fields, Karachaganak and Kashagan, for most of its

production, is subject to output targets as a member of OPEC+,

an alliance of OPEC and other top producers led by Russia.

The production decline may help Kazakhstan comply with

its output quota under an agreement with the OPEC+ group.

One of the sources said production has declined due to

maintenance at the field. The operator of Tengiz did not

immediately respond to a request for comment.

Tengiz boosted oil output to a record high in early October

to 699,000 bpd from 687,000 bpd in September, when output

increased by 30% from August after the completion of

maintenance.

Chevron ( CVX ) and its partners plan to expand output at the Tengiz

project to 850,000 bpd in the first half of 2025. Expansion

costs at the project stand at around $49 billion.

Chevron ( CVX ) owns a 50% stake in the venture. Exxon Mobil ( XOM )

controls 25%, KazMunayGaz has a 20% stake, and

Russia's Lukoil owns 5%.

Kazakhstan's average daily oil output in October was down

20% from September, complying with the country's OPEC+ quota,

according to Reuters calculations.

The output was about 150,000-185,000 bpd lower than the

country's OPEC+ quota of 1.468 bpd, depending on the ratio used

for the conversion of tons into barrels.