“For the rest of this decade there has to be a big question of how far Europe can rely on North African gas,” said Jonathan P. Stern, chairman of the gas program at the Oxford Institute for Energy Studies, a research concern. “It certainly can’t rely on an expansion of North African gas supplies. Most likely there will be a contraction.”

During the militants’ attack on In Amenas, and the Algerian military’s action to retake the facility, 40 workers and 29 insurgents were killed. The plant — jointly owned by BP, Statoil of Norway and Sonatrach, the Algerian national energy company — has yet to reopen. Its gas field and processing center accounted for about 10 percent of Algerian production, but so far the shutdown has had little impact on exports.

“Algeria still has the ability to swing production for short periods,” said Femi Oso, an analyst at Wood Mackenzie, an energy consulting firm in Edinburgh.

Algeria reinjects a substantial portion of its gas back into its oil and gas fields to maintain pressure. Mr. Oso said that Sonatrach is now diverting some of this gas into exports, but this is only a short-term fix.

Sonatrach is pressing to repair and reopen the plant, which suffered blast damage.

But if much of the plant remains closed for long, or if there is another attack on Algeria’s energy production infrastructure, exports will suffer, analysts say, forcing up prices in Europe. Most of the Algerian and Libyan gas exported to Europe flows under the Mediterranean through a handful of giant pipelines. While the undersea portion of these arteries seems secure, the pipelines cover long stretches of desert before they reach the sea. Some pass through troubled countries like Tunisia, where they could be hit.