A certificate of origin determines whether a shipment qualifies for preferential duty treatment inside the GCC. Getting the issuing authority wrong is a common, avoidable cause of a shipment being reassessed at full duty.
What the certificate actually proves
A certificate of origin declares the country where goods were produced or substantially transformed, and within GCC intra-regional trade this determines whether goods move duty free between member states as originating goods, or whether they are treated as third country imports subject to the common external tariff.
For goods moving between Turkey and Oman, the certificate establishes Turkish origin for the purposes of whichever trade agreement or preferential arrangement applies, and an incorrect or missing certificate defaults the shipment to standard duty treatment.
Who is authorised to issue it
In Turkey, certificates of origin for export are issued by the local Chamber of Commerce, not by the exporting company itself, and the certificate must reference the correct HS code and trade agreement to be accepted at the Omani side.
A certificate issued under the wrong agreement reference, or one missing the chamber's authentication, is treated by Omani customs as unverifiable and the shipment reassessed at standard rates rather than the preferential rate the exporter expected.
The practical checklist before shipping
Confirm the certificate references the correct HS code, the correct trade agreement or preferential arrangement, and carries the issuing chamber's authentication stamp, before the shipment leaves Turkey, since correcting any of these after departure means the goods sit at the Omani port pending reassessment.