Saudi Aramco extends bids for Yanbu refinery unit

* Yanbu accounts for nearly a quarter of expansion plans

* New deadline for coker unit bids is Aug. 9

* Cost of project has fallen

KHOBAR, Saudi Arabia, July 22 (Reuters) - State oil giant Saudi Aramco has asked firms to extend the deadline for bids to build one of the units at the 400,000 barrels per day (bpd) Yanbu refinery, industry sources said on Thursday.

The Yanbu project accounts for just under a quarter of the country's planned expansion of around 1.7 million bpd of refining capacity on top of the current 2.1 million bpd.

The state-run firm [SDABO.UL] had previously asked engineering firms to extend the validity by 60 days to July 26 for bids for contracts for the Yanbu project.

The deadline has been pushed back further for the coker unit, the sources said, but it remains unchanged for other units.

"Aramco asked to extend validity date of package 1 to Aug. 9," an industry source said.