A Chevron Corp. unit will start on May 9 to shut oil fields Saudi Arabia is developing jointly with Kuwait after parties failed to resolve differences to keep the project running, according to two people with knowledge of the matter.

Saudi Arabian Chevron sent a letter to Kuwaiti officials setting the date for employees at the Wafra onshore fields on Kuwait’s side of the shared border with Saudi Arabia to begin withdrawing and shutting down facilities, said the people, who asked not to be identified because the information is confidential. The project has been hampered by a lack of staff and adequate imports of equipment after the Kuwaiti government stopped issuing or renewing permits last year, they said.

“Current difficulties in securing work permits and materials may impact the company’s ability to safely continue production. Efforts continue with all appropriate parties to resolve the issue,” Sally Jones, Chevron spokeswoman in London, said by email on Tuesday. “It is not Chevron’s policy to comment on industry speculation,” she said, regarding the May 9 date for the start of shutdown. Officials at state-run Kuwait Petroleum Co. didn’t answer phone calls for comment.

Chevron’s plan to shut down the onshore fields at Wafra follows Saudi Arabia’s Oct. 16 halt in operations at the Khafji offshore deposits, which also lie in the shared Saudi-Kuwaiti border zone, on environmental concerns. Wafra and Khafji each has a crude production capacity of 250,000 barrels a day. The developments come as Saudi Arabia, Kuwait and other OPEC members are under increasing pressure to scale back output amid a global supply glut and slower demand growth.

Saudi Chevron

Crude output at Wafra, where Saudi Chevron is the operating company, has dropped 20% since October to 180,000 barrels a day, two people with knowledge of the matter said Feb. 9. The project, in which Chevron had planned to invest as much as $40 billion, is one of the world’s largest attempts to free heavy oil by injecting steam underground.

Saudi Arabia, the largest producer in OPEC, and Kuwait, the group’s third-biggest member along with Iran, will join other OPEC states to assess market conditions and production levels at a June 5 meeting in Vienna. OPEC, which supplies 40% of the world’s oil, raised production by 481,000 barrels a day to 31 million in March, according to data compiled by Bloomberg.