The majority stake in Yanhua is still owned by the state-controlled Sinopec Corp., but 30 percent of Yanhua’s shares are traded publicly on the New York and Hong Kong exchanges.

Sinopec’s complex internal governing structure—and its murky relationship to the Sudanese government—have befuddled analysts for years.

“The way that Sinopec fits into all this, I think will be very, very difficult to uncover,” Reeves said.

In the run-up to the initial public offering (IPO) of Sinopec stock on global exchanges in October 2000, the company weathered criticism from human rights activists over its small stake in a Sudanese oil exploration block. Sinopec sold the Sudanese holding to CNPC before the IPO, company officials said at the time.

But Reuters reported in October 2004 that Sinopec had purchased a six percent stake in two Sudanese oil blocks in the eastern Upper Nile region of the country. And the Washington Post reported in December that Sinopec is constructing a pipeline connecting the Melut Basin, in the south of Sudan, to a tanker terminal on the Red Sea.

Once the pipeline from the Melut Basin is up and running, revenues will be shared by the Khartoum regime and the rebel-led government of South Sudan, said Jemera Rone, a researcher at Human Rights Watch in Washington, D.C. Until a final peace accord is reached ending the two-decade-long Sudanese civil war, the South’s share of oil revenues will accrue interest in an escrow fund, Rone said.

—Staff writer Daniel J. Hemel can be reached at hemel@fas.harvard.edu.