(Bloomberg) -- Russia’s oil processing in early December fell to a seven-week low as logistical constraints weighed on refineries.

The nation’s plants processed 5.33 million barrels of crude a day in the first six days of the month, down about 81,000 barrels a day from the prior week’s average, according to a person with knowledge of industry data. That’s a second week of decline and the lowest rate since the second half of October, Bloomberg calculations show.

Several major refineries in three areas — southern and central Russia and the Volga region — led the downturn, the person said, asking not to be identified as the information isn’t public.

Declines were noted at Rosneft PJSC’s Tuapse, Ryazan and Saratov plants, at Lukoil PJSC’s Volgograd, Nizhny Novgorod and Perm facilities and at Surgutneftegas PJSC’s Kirishi site, the person said. Cuts were mainly due to logistical constraints that were aggravated by a recent storm in the Black Sea, a key route for fuel exports, the person said.

Those companies, and the press service for Russia’s Energy Ministry, didn’t immediately respond to requests for comment.

Read More: Black Sea Storms Batter Russian Crude Exports to Three-Month Low

Traders and analysts scrutinize refining rates as one of the key remaining gauges — together with seaborne crude exports — to assess Russia’s oil production after Moscow classified official output data amid Western sanctions.

The country’s seaborne oil shipments in the week to Dec. 3 dropped to 2.74 million barrels a day amid Black Sea storms. That’s down by about 500,000 barrels a day from the revised figure for the week to Nov. 26, according to tanker-tracking data monitored by Bloomberg. Shipments were the lowest in 15 weeks.

Russia has pledged to cut its combined crude and petroleum-product exports by 300,000 barrels a day through year-end in a move to stabilize the global energy market. 

In the first quarter of next year, the nation is set to deepen those curbs to 500,000 barrels a day in a step coordinated with the Organization of Petroleum Exporting Countries and its allies. Russia will start implementing those reductions this month and reach pledged volumes in January, Deputy Prime Minister Alexander Novak told state news agency Tass last week.

©2023 Bloomberg L.P.