MOSCOW, April 17 (Reuters) - Black Sea CPC Blend oil

exports via the Caspian Pipeline Consortium (CPC) pipeline

system are set to decline to about 4.9 million metric tons in

May from 5.4 million planned for April, three sources familiar

with the matter said.

On a daily basis CPC Blend oil exports will decline by some

12% in May from April's plan, Reuters calculations showed.

A drop is expected due to planned maintenance on the Tengiz

oilfield, the sources said, while it was not clear when the work

would take place or how long it would take.

The expected decline in exports has already supported prices

of CPC Blend oil cargoes loading next month.

Chevron ( CVX )-led Tengizchevroil, the Tengiz oilfield's operator,

and the Kazakh Energy Ministry did not reply to Reuters'

requests for comment.