State-run Saudi Aramco has revived bidding for a cleaner fuels project at its biggest oil refinery in Ras Tanura, sources familiar with the plan said, following speculation that lower oil prices would force the project's cancellation.

The potential $2 billion scheme has had at least three previous rounds of bidding without a contract being awarded.

It has now been communicated to contractors that the fresh due date for bids is in May, the sources said, with one adding an award was expected in August.

Aramco didn't respond to a request for comment.

Saudi Aramco has been revamping its refineries to produce cleaner fuels, as part of a trend at Middle Eastern refineries to target export markets with stricter environmental requirements.

The Ras Tanura clean fuels project, including a naphtha hydrotreater, was to be part of a second phase of upgrades and was originally due to go on stream in 2016. - Reuters