AP PetroChina Factory in Jilin, China (2005 File Photo)

Warren Buffett's Berkshire Hathaway has once again trimmed its stake in PetroChina.  The sale of 28 million shares for roughly $40 million further reduces his stake to 8.93 percent from just over 11 percent earlier this year.

It's the third reported sale in recent months.  About a week ago we learned that Berkshire had sold about $136 million dollars worth of PetroChina and back in July there was a filing for a $27 million sale.

(Editor's Note: There's an update to this post filed a few hours later.  Read how Buffett has been selling more PetroChina shares than you might have thought.)

The selling comes amid calls by human-rights activists for Buffett to divest from PetroChina due to the government-controlled company's ties with Sudan.  Critics say PetroChina's "extensive involvement" with Sudan's oil industry makes it harder to pressure the Sudanese government about the humanitarian crisis in the Darfur region.  A group calling itself Investors Against Genocide is trying to organize letter-writing campaigns to Berkshire and other PetroChina holders urging them to "change their investing strategy so as to avoid complicity in genocide."

Buffett has rejected those calls in the past, and many analysts are saying he's now locking in  profits after PetroChina's 12 percent gain since the beginning of the year, and the even larger gains since he bought the shares several years before.

In an interview with the Omaha World-Herald in March, Buffett said he couldn't influence the Chinese government if he wanted to. "I can be a direct descendant of William Jennings Bryan, but I will not be changing the Chinese government's policy.  I doubt I could change the policies of the Douglas County Board."  Buffett also called the situation in Darfur "deplorable" and said he sympathiezes with those trying to address the Darfur problem.  But, when it comes to advocating divestment, "They're on the wrong area in terms of actually getting anything done."

Even so, in a statement on its web site, Investors Against Genocide's Eric Cohen writes that "we are encouraged" by Berkshire's sales of PetroChina stock.

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