With an official natural gas storage plan by the European Union (EU) in hand, member countries are bearing down on filling reserves while the market keeps a wary eye on volumes from Russia and U.S. liquefied natural gas (LNG) producers.

The European Commission (EC) solidified on Monday a plan that directs storage facilities in member states to reach 80% of capacity by November. Following that target, EU storage is expected to reach 85% by the end of the year and then 90% for the following winter.

Kadri Simson, European Commissioner for Energy, said the rule should send “a very clear message” to European and international energy companies on the need to act for the bloc’s security. However, she also acknowledged the hard road ahead for member states already impacted by gas...