Oil exports via the Caspian Pipeline Consortium, which brings crude from Kazakhstan to a Russian terminal in the Black Sea, dropped by 24 per cent in December from the previous month following drone attacks, an industry source familiar with the data told Reuters on Friday.
CPC handles around 1.5 per cent of global oil and accounts for 80 per cent of Kazakhstan's oil exports.
Shareholders in CPC's 1,500-km (930-mile) pipeline include Kazakhstan's state-owned oil company Kazmunaygas, Russia's Lukoil and units of US oil giants Chevron and ExxonMobil.
Exports declined in December from November to 3.98 million tonnes, or around 1.02 million barrels per day, according to the source.
The drop in December contrasted sharply with a rise in exports in previous months in 2025 as production at Kazakhstan's oilfields increased.
Flows rose by around 12 per cent to a record 70.5 million tonnes, or around 1.5 million barrels per day, in 2025, the source said.
CPC did not immediately respond to a request for comment.
Kazakhstan's Energy Ministry said on Tuesday that the country reduced oil shipments through the CPC marine terminal in December because of drone attacks and adverse Black Sea weather conditions. It did not provide details.
On November 29, drones severely damaged CPC's exporting equipment on the Russian Black Sea coast, resulting in a fall in oil exports via the pipeline. Kazakhstan blamed the attack on Ukraine, which has been targeting Russian energy infrastructure to pressure Moscow to end its war in Ukraine.
Ukraine said its actions were not directed against Kazakhstan but were aimed at repelling what it called "full-scale Russian aggression".
This week, unidentified drones struck at least two oil tankers in the Black Sea on Tuesday, including one chartered by Chevron, as they sailed toward the terminal on the Russian coast.
Kazakhstan redirected 300,000 tonnes of oil away from the CPC in December, Kazmunaygas said earlier on Friday, as exporting equipment was damaged by a drone attack.
(Reporting by Reuters; Editing by Mark Potter and Susan Fenton)