The OPEC deal has proved it's value: OPEC members reduced their exploration activity. With the growing demand it accelerates market balancing and stimulates growth in oil prices. However, the main goal of the agreement (reducing commercial reserves below 5-year average) is not yet achieved. This motivated OPEC to extend the deal througout 2018. [Own translation]
Original article was published in Oil and Gas Vertical Magazine (Russia), issue 1, January 2018. The full release in Russian language can be retrieved here.