MOSCOW, May 6 (Reuters) - Oil output at Kazakhstan's

giant oilfield Tengiz, operated by Chevron ( CVX )-led

Tengizchevroil, declined by 25% over May 1-5 from April's

average level to 474,000 barrels per day (bpd), a source

familiar with the data told Reuters on Monday.

Tengizchevroil planned to conduct scheduled maintenance at

one of six production trains at the Tengiz oilfield this month.

The Caspian Pipeline Consortium will likely cut CPC Blend

oil exports in May to 4.9 million metric tons from 5.4

million tons in April due to the maintenance, industry sources

have said.

Both Tengizchevroil and the energy ministry did not

immediately respond to requests for comment.