China’s commercial crude oil stocks at the end of December fell almost 4 percent from the previous month and refined fuel stocks were also down 4 percent, the official Xinhua News Agency reported on Monday.

However, diesel stocks rose 13.6 percent due to weak industrial demand, China Oil, Gas & Petrochemicals (OGP), a Xinhua newsletter, reported.

Diesel demand may have posted its first fall in more than a decade in 2014. State oil giant Sinopec, which accounts for almost half of China’s refinery throughput, said its diesel production fell 4 percent in 2014.

Gasoline stocks recorded a 4.3 percent decline in December as low oil prices helped stimulate demand even though consumption is traditionally lower in winter, the newsletter said.

Stocks of kerosene, used mostly as aviation fuel, fell 3.2 percent from last month.

Refiners have begun boosting jet fuel output at the cost of diesel to meet growing demand.

Crude stocks, excluding the country’s strategic reserves, fell 3.9 percent from the month before, China OGP said.

December saw record imports of crude oil and record domestic crude production. Analysts say China is probably taking advantage of low oil prices to build its strategic petroleum reserves (SPR).

China said in November it was holding 91 million barrels in the first phase of its strategic reserves, but generally it rarely releases such information.

Last month, domestic refinery crude throughput rose 2 percent from November to 10.5 million barrels per day.

The following table shows China’s commercial stockpiles in millions of metric tonnes, calculated by Reuters based on monthly percentage change data released each month in China OGP.

The publication stopped reporting outright volumes in July 2010. It does not include strategic reserves and may also not include reserves held by the state-owned oil majors for strategic purposes.