BEIJING, Jan. 13 -- Lock-up shares worth 20.83 billion yuan (3.41 billion U.S. dollars) will become eligible for trade this week on the Chinese mainland.

The volume is less than half of the 50 billion yuan in shares that became eligible between Jan. 6 and 10, according to information from the Shanghai and Shenzhen stock exchanges.

Altogether 25 listed companies on the two stock exchanges will see lock-up shares released to capital markets this week.

Under the mainland's market rules, major shareholders of non-tradable stocks are subject to one or two years of lock-up before they are permitted to trade.

Sinovel Wind Group Co., Ltd., a leading wind turbine producer, will see shares worth about 7.24 billion yuan become available -- the most of any company this week.