The order has been placed by Aramco Overseas Company (AOC) and Dow Europe Holding BV.
The PO unit will be part of a fully integrated chemicals complex.
The chemicals complex will be built, owned and operated by Sadara Chemical Company, a joint venture between Saudi Aramco and Dow.
The contract has been awarded as an extension to the front-end engineering design contract awarded to Foster Wheeler by AOC and Dow in 2008.
The PO unit is expected to be completed during the first quarter of 2015.