(Bloomberg) -- The Democratic Republic of Congo increased the number of oil and gas permits up for auction this month, including in an area that overlaps with the Virunga UNESCO World Heritage site and blocks previously held by Israeli billionaire Dan Gertler. 

The call for offers is set to take place July 28 and 29 in the capital, Kinshasa, and will now encompass 27 oil blocks and three gas permits, the oil ministry said in a statement Monday. The ministry previously planned to offer a total of 16 concessions. 

The government added the new permits to the auction to “maximize the opportunity for the country within the framework of this process,” the ministry said in the statement. 

Congo plans to use the auction to grow its small oil industry, which only produces about 25,000 barrels a day from a project in the west of the country run by France’s Perenco SA. The process has drawn criticism from environmental groups for offering blocks that overlap with Congo’s peatlands, which are among the world’s most important carbon sinks. 

The peatlands store about 30 billion tons of carbon -- equivalent to about 82% of annual global carbon-dioxide emissions. So-called carbon sinks help mitigate greenhouse-gas emissions from burning fossil fuels and other activities. The oil ministry has previously said it would be “taking into account the environmental sensitivities” of the permit areas, which stretch across sub-Saharan Africa’s largest country by landmass.

Read: Congo’s Oil Block Sale Threatens Carbon Sinks, Forest Pact

The additional blocks could add to the controversy, particularly Blocks 4 and 5, which overlap with Virunga National Park, the UNESCO World Heritage site. The park is home to about a third of the world’s endangered mountain gorillas. 

London-based Soco International Plc gave up on Block 5 in 2015 under pressure from environmental groups. A 2014 film on the controversy was nominated for an Academy Award for best documentary feature.

The two blocks formerly owned by Gertler could be among the most valuable assets up for auction. A representative for the billionaire, who is under US government sanctions for alleged corruption in Congo, confirmed Tuesday that he had relinquished the permits as part of a March deal with the government. 

Congo has previously spoken to companies including Tullow Oil Plc, TotalEnergies SE and Eni SpA about taking over the blocks, which are adjacent to those on the Ugandan side of Lake Albert under development by Total, China’s Cnooc Ltd. and the state-owned Uganda National Oil Co. 

Any development of the blocks will likely need to tap into a planned pipeline on the Uganda side, which will transport oil 1,443 kilometers (896 miles) from the country’s oil fields to Tanzania’s port of Tanga. 

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The gas permits are on Lake Kivu along Congo’s eastern border with Rwanda, which is already exploiting the abundant methane gas found beneath the lake. 

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