Orpic operates Mina Al Fahal Refinery in Muscat, Sohar Refinery, and polypropylene and aromatics plants in Sohar.
Financial details of the deal have not been disclosed.
Amec Foster Wheeler will offer specialist process, technology engineering support, process safety improvement and maintenance programme support for the refineries and chemical plants.
The engineering firm will also arrange an expert helpdesk service to provide trouble-shooting advice for the plant processes and optimise their production.
Amec Foster Wheeler Group president for Asia, Middle East, Africa and Southern Europe Roberto Penno said: "This contract opens up exciting opportunities for us to deliver for a new client in a growth region.
"The agreement covers a wide range of our capabilities including increasing optimisation and we look forward to being able to demonstrate and deliver our capabilities for Orpic."
Amec Foster Wheeler is expected to bring down the costs for energy and utilities usage at the Orpic facilities, and boost their reliability, safety and environmental performance.
The firm will integrate local Oman skills with its service from Reading, UK.
