The EU’s eastern members will be among the countries worst affected in case of a prolonged interruption of Russian gas supplies this winter, the European Commission has said.

In a report on the resilience of the European gas system issued on Thursday the EU executive body concluded that if member states cooperate and allow the market forces to work as long as possible, gas will continue to be delivered to companies and households.

Highlighting that the dispute between Moscow and Kiev over gas prices and unpaid debt for past deliveries puts Russian gas supplies to the EU once more at risk, as in 2009, the Commission said it had analysed different scenarios, in particular a complete halt of Russian gas imports into the EU for a period of six months and a disruption of Russian gas transitvia Ukraine for a period of one or six months.

“In the absence of cooperation between Member States and of additional national measures, serious supply shortfalls of 40% or significantly more could materialise,” at least towards the end of an assumed  six-month disruption period, for Bulgaria, Romania, Serbia, and Bosnia and Herzegovina (in both Ukraine transit and full Russian supply disruption scenarios), the Commission’s stress tests have shown.

Shortfalls of similar magnitude would apply for Lithuania, Estonia and Finland in the scenario of a total halt of Russian supplies to the EU, while Hungary and Poland would be affected by deficits of 30% and 20%, respectively.

“In the cooperative scenario the effects of the disruption are significantly dampened” in those EU member states and the countries of the former Yugoslav Federation most affected, particularly Bulgaria, Estonia, Bosnia and Herzegovina, Macedonia and Serbia.

“At the same time Greece and Latvia would likely also experience some non-negligible shortfall,” the report said.

The Commission concluded that if countries work together, instead of adopting strictly national measures, then less consumers will be cut off from gas supplies.

“In this scenario, no household in the EU would have to be affected,” the Commission said.

It added that non-market measures such as the release of strategic stocks, forced switching to alternative fuels and demand curtailment should only be imposed when the market fails.

Based on the analysis of the stress tests, the Commission said that countries should follow a market-based approach and avoid interventionist measures as well as increase energy coordination with each other including through maximisation of interconnector capacity and abandoning restrictions to cross-border energy trade.

According to Commission data, the EU imports 53% of the energy it consumes including about 90% of oil and 66% of natural gas. Forty-eight percent of the EU's primary energy consumption is spent on space and water heating.