The leadership reshuffle at the People's Bank of China (PBOC) is closely watched in global financial markets as monetary policy changes and any moves to further liberalise the financial system of the world's second-large economy would have repercussions well beyond China's shores.
The 69-year-old Zhou has spearheaded financial reforms and boosted the yuan currency's global clout, as well as the central bank's policy influence, since taking up his post in 2002.
Zhou is likely to retire around the time of the annual session of parliament next March, according to the seven sources with ties to the leadership and close to the central bank.
Guo, chairman of the China Banking Regulatory Commission (CBRC), whose rich experience and reformist credentials are similar to Zhou's, is seen as more qualified for the job, the sources said.
However, Jiang, the Communist Party chief of Hubei province, has the backing of some top leaders and is seen as having a roughly equal chance of getting the post, they noted.
The PBOC and the CBRC did not respond to Reuters' requests for comment, while officials at Hubei Communist Party committee's propaganda department declined to comment.
Yi Gang, 59, a PBOC vice-governor who has a PhD in economics from the University of Illinois, is the leading in-house candidate to replace Zhou but is not seen as a frontrunner.
Yi is a well-trained economist who is supported by Zhou, but his background as a "sea turtle" - a colloquialism for Chinese who have returned from overseas - means he is less likely to gain the full trust of China's leaders, the sources said.
One of the sources, who correctly predicted a reshuffle of the country's top banking, securities and insurance regulators in 2011, said that Guo is most favoured, helped by his understanding of the financial markets and the global economy.
"His appointment would boost confidence," the source added.
NO DARK HOUSE
Guo, 61, was summoned back to Beijing in February to lead the CBRC after serving as governor of Shandong province for four years - his second regional stint after serving as a deputy governor of Guizhou province in the late 1990s.
Under Guo's leadership earlier this year, the CBRC started what was widely dubbed a "regulatory windstorm" to force banks to cut debt, but he later eased up after the move fuelled fears of a liquidity crunch.
Guo, a philosophy major and once a visiting scholar at Oxford University, has served as a deputy central bank governor and as the top foreign exchange regulator, and steered China Construction Bank Corp (>> China Construction Bank Corporation)<0939.HK> to a successful share listing. As a top stock market regulator, Guo cemented a reputation as an economic reformer.
Still, Jiang, who has also alternated between top financial and provincial posts, remains a formidable challenger for Guo, the sources said.
The 60-year-old Hubei party chief, who has had stints as an assistant central bank governor and head of China Development Bank, the country's largest policy bank, emerged as a possible successor to Zhou relatively recently.
Jiang has been credited with helping to transform the state-owned Bank of Communications (>> Bank of Communications Co Ltd) <3328.HK>, which had been plagued by bad debt, into a bank with a stronger balance sheet that then listed in Hong Kong and Shanghai.
"Jiang is not a dark horse, his resume is very good and he has been proved to be very capable," said one of the sources.
Whoever takes the helm of the central bank will face tough challenges as he will have to walk a tightrope between ensuring economic stability and pushing reforms to rein in debt risks.
Zhou has been steering broad financial and currency reforms, loosened controls on interest rates and moved away from what had effectively been a yuan peg to the U.S. dollar - a step along the path to turning it into a global currency on a par with the greenback.
"In terms of international investors, Guo may offer more continuity," said Rob Subbaraman, Nomura's chief economist and head of global markets research for Asia-ex-Japan.
"That's really what he represents - continuity of wanting to, over time, move to a more liberalised capital and financial market, and trying to ensure very good regulation and supervision."
Zhou stayed on past retirement age after he was appointed a vice chairman of the top advisory body to parliament in 2013, a move that made him a national leader.
The PBOC still has limited policy independence despite growing influence under Zhou.
Unlike western central banks, the PBOC does not have the final word on adjusting interest rates and the value of the yuan. The basic course of monetary and currency policy is set by the cabinet or by the Communist Party's ruling Politburo.
(By Kevin Yao and Benjamin Kang Lim; Edited by Martin Howell)
By Kevin Yao and Benjamin Kang Lim