State firm Qatar Petroleum (QP) plans to merge two petrochemicals affiliates in a bid to cut costs and boost efficiency. Qatar Vinyl Company (QVC) will be integrated into Qatar Petrochemical Company (Qapco), which is owned 80% by QP-led Industries Qatar and 20% by France’s Total.

QVC’s shareholders are QP’s Mesaieed Petrochemical Holding Company (MPHC) with 55%, Qapco with 32% and QP with 13%. QP says the merger will not change QVC’s ownership, but will “allow...