Experts said the tender, which also covers blocks in the Bohai Sea off north China and in the East China Sea, was probably the largest offered by China National Offshore Oil Corp (CNOOC) since the 1990s, in the latest sign the oil giant wants to beef up exploration as its output growth slows.
The tender comes two months after CNOOC invited international firms to bid for nine blocks in the western part of the South China Sea, a move Vietnam said was illegal as the blocks encroached on its territorial waters.
China at the time insisted the tender in June was in accord with Chinese and international law and urged Vietnam not to escalate the quarrel.
Huang Xinhua, a geologist at energy consultancy IHS, said none of the latest blocks appeared to be in disputed areas.
One of the blocks is in the northern Bohai Bay, with three in the East China Sea, 18 in the eastern part of the South China Sea and four in the western South China Sea.
The three deep-water blocks in the eastern part of the South China Sea are at depths between 700 and 3,000 metres, it said, adding that foreign firms have until Nov 30 to view data packages for all the blocks tendered.
"The tender should be CNOOC's largest in terms of the number of blocks offered since the 1990s, showing CNOOC really wants to beef up its exploration in offshore China with the help of international firms," Huang said.
The three deep sea blocks, which cover a total of 15,365 square kilometres, as well as acreage in the Qiongdongnan basin in the western part of the South China Sea were among the most attractive as hardly any drilling has been carried out there so far, Huang added.
CNOOC, parent of CNOOC Ltd , normally teams with foreign firms to explore for oil and gas offshore, but once a commercial find is made the firm holds the right to take a 51 percent stake.
Beijing claims almost all the South China Sea, a body of water believed to hold rich reserves of oil and gas and which stretches from China to Indonesia and from Vietnam to the Philippines. Vietnam, the Philippines, Taiwan, Brunei and Malaysia claim parts of it.