By Kate Abnett
BRUSSELS (Reuters) - European Union countries will this week debate a possible deal to share out the costs of buying gas to fill storage and build a supply buffer ahead of next winter, according to a draft document seen by Reuters.
EU countries are negotiating proposed rules that would require them to fill their gas storage to at least 90% of capacity by Nov. 1 each year from 2023 and 80% this year - an attempt to reduce the leverage of Russia, which supplies around 40% of EU gas.
The proposal had worried some states with gas storage, including Hungary, Austria and the Netherlands, which feared their companies would be forced to buy large volumes of gas at near-record prices, while those in countries with little or no storage would not.
Diplomats from EU countries will this week discuss a compromise deal, which if approved could lead to negotiations with European Parliament on the final rules.
The draft proposal would keep the 90% target, but only apply it to storage sites that serve the host country's domestic consumers - meaning a state would not be obliged to fill gas storage on its territory that is mainly used by another country.
A country's contribution to filling storage would also be capped at 35% of its average annual gas consumption over the last five years, under the proposal by France, which currently chairs meetings of EU countries.
Stored liquefied natural gas could count towards the targets.
The EU has vowed to quit Russian fossil fuels by 2027 in response to Moscow's invasion of Ukraine, but for now Europe relies on Russian gas. The storage rules would aim to provide a buffer in case of disruptions to that supply.
Countries would be responsible for ensuring their storage is filled, which they could do by imposing measures such as obligations for gas suppliers to store minimum volumes.
To soothe concerns about sharing the costs fairly between states, Brussels had proposed a "burden sharing" system where countries without storage sites must cover 15% of their annual gas use by filling equivalent storage in other states.
The French proposal said if this is not possible, countries could meet an equivalent storage obligation through different fuels like oil.
The proposal also said a country that is the main user of a storage site in another state should be obliged to fill that site with equivalent to its average annual use of the facility over the last five years.
The draft would exempt Cyprus, Malta and Ireland from the targets - island countries that had been concerned they would be forced to pay for gas supplies they wouldn't use, since they are not connected to other countries' storage sites.
(Reporting by Kate Abnett; Editing by John Chalmers and Susan Fenton)