Anglo-Australian Rio Tinto (ASX:RIO) says it has completed a 100 per cent divestment of its equity holdings in US collier Cloud Peak Energy Inc. through a fully exercised over allotment in connection with a recently announced secondary offering.

Underwriters exercised their option to purchase 3,800,000 additional shares of Cloud Peak Energy Inc's common stock for US$19.50 per share, Rio said in a statement on Thursday.

The secondary offering of 25,600,000 shares and the over allotment closed on December 21, 2010. Gross proceeds from the over allotment were US$74.1 million, bringing the total gross proceeds from the secondary offering to US$573.3 million.

Rio Tinto continues to have certain rights under the tax receivable agreement entered into with Cloud Peak at the time of the initial public offering.