The technical bids were opened at the Tender Board on Monday.
The tender for the EPC contract of the expansion project was floated in December 2012 following a pre-qualification process. Around 50 companies had applied for pre-qualification in December 2011, and nine were pre-qualified in August 2012.
The companies that have submitted offers are: The joint venture (JV) of South Korea's GS Engineering & Construction and Indian engineering giant Larsen & Toubro; JV of South Korea's Daelim Industrial Co and London-based Petrofac; JV of Hyundai Engineering & Construction and Hyundai Engineering Co, South Korean firm S K Engineering and Construction; JV of Samsung Engineering Co Ltd and Japanese engineering corporation Chiyoda, and Tecnicas Reunidas, a leading Spanish engineering firm.
Among the nine companies shortlisted during the pre-qualification process, Japan's JGC Corp and Daewoo Engineering & Construction of Korea withdrew earlier, while Technip France did not submit its offer.
The expansion project is expected to improve the Sohar refinery's product quality and increase refining capacity by more than 70 per cent to add another 60,000 barrels per day of oil to its current capacity.
The expansion, which is estimated to cost between US$1.5-US$1.8bn, is expected to be completed by the first half of 2016.
The project will be implemented at the Sohar Industrial Port to complement the existing refinery, which was commissioned in 2006.