(Reuters) - China has issued its second batch of refined fuel export quotas for 2024, totalling 18 million metric tons, Chinese consultancies and trade sources said on Tuesday.

The volume is 2 million tons more than the second batch issued last year and could boost fuel supplies and further depress refining margins in Asia.

The export volumes, comprising 14 million tons of refined products and 4 million tons of marine fuel, were allotted primarily to state-owned refiners, according to consultancies Longzhong and JLC and the trade sources.

The new quota brings this year's total for exports of refined and marine fuels to 45 million tons, following the first 27-million-ton batch issued at the start of January.

"The increased volume year on year is likely due to higher demand for jet fuel from the aviation bunkering sector, which is also counted as exports," Emma Li, an analyst at shiptracking firm Vortexa said.

China could also issue smaller batches for the rest of the year to avoid a large year-on-year rise, she added.

March exports for the aviation fuel were near a four-year high, customs data showed, while traders expect May shipments to breach the 2 million ton level again.

Beijing manages its refined oil exports via a strict quota system, using exports as a tool to balance and ensure the domestic market is sufficiently supplied.

State oil companies Sinopec and PetroChina, the top recipients of the quotas that cover diesel, gasoline and aviation fuel, together were granted 9.98 million tons or more than 70% of the total, according to the two consultancies.

Private refiner Zhejiang Petrochemical Corp was allotted 1.22 million tons, while a refinery subsidiary of state defence conglomerate Norinco and China National Aviation Fuel Company were assigned 230,000 tons in total.

China's Ministry of Commerce did not immediately respond to a faxed request for comment.

(Reporting by Trixie Yap, Chen Aizhu, Jeslyn Lerh and Florence Tan in Singapore, Andrew Hayley in Beijing; Editing by Sonali Paul and Eileen Soreng)

By Trixie Yap and Andrew Hayley