Aug 9 (Reuters) - Kazakhstan's biggest oil producer,

Chevron ( CVX )-led Tengizchevroil (TCO), started scheduled

maintenance at two of its six production lines on Aug. 1, the

company said on Friday.

TCO did not say how the maintenance affected its output or

how long it would last, but sources familiar with the data told

Reuters its average daily output in the first week of August

fell 14% compared with July to 68,660 metric tons.

(Reporting by Alla Afanasyeva

Writing by Olzhas Auyezov

Editing by David Goodman

)