(Bloomberg) -- Russia’s overseas shipments of diesel slumped sharply in the initial days after Moscow banned exports, data from a shipping analytics firm show.

There had been some trader skepticism about how aggressively Russia would enforce a measure that could deprive the world of one of the key sources of the automotive and industrial fuel.

However, data from analytics firm Vortexa Ltd. indicate that flows fell 57% after the government imposed the ban to allow more supplies for the domestic market. Observed outflows of diesel dropped to about 207,000 barrels from Sept. 21 until the end of the month. That compares with about 479,000 barrels a day in the period from Sept. 1-20.

Even market specialists can find it challenging to filter diesel from what can be near-identical gasoil with absolute certainty. The latter product is not banned. Taken as a whole, shipments of both diesel and gasoil fell by 36%, according to Vortexa.

Traders and analysts are closely monitoring Russia’s oil exports to gauge production, after the government classified official output data. Diesel and gasoil exports were already expected to be lower in September due to refinery maintenance. Moscow eased the ban several days after its announcement, though most diesel flows are still prohibited.  

Read more: Russia Mulls Lifting Diesel Export Ban Only for Fuel Producers

Despite the diesel slump, Russia’s total exports of petroleum products actually increased by about 7% last month, to 2.43 million barrels a day. That’s due to greater flows of naphtha, a light-end product used to make gasoline, and dirtier fuel oil, often used in shipping and secondary refining feedstocks.

Naphtha exports soared by 64% on a monthly basis, to about 560,000 barrels a day — the highest level since March. The bulk of the cargoes sailed for Asia, followed by Africa.

Fuel oil, which accounted for almost a third of overall flows, surged 19% on a monthly basis to 763,000 barrels a day. Exports of refinery feedstocks like vacuum gasoil gained to a four-month high of 128,000 barrels a day.

Shipments of gasoline and blending components slumped to an 11-month low at 77,000 barrels a day. Jet fuel flows declined to just 29,000 barrels a day, the lowest since July.

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