Berkshire Hathaway Inc. Chairman Warren Buffett...will be confronted by Darfur protests at this year's gathering... [Some shareholders want] Buffett to divest $3.3 billion of stock in PetroChina Co., controlled by China National Petroleum Corp.,...[which] holds oil reserves and pipelines in Sudan... Buffett has opposed selling and says PetroChina has no influence over its parent... Liu Weijing, a...spokesman for China National Petroleum, declined to comment. Mao Zefeng, PetroChina's head of investor relations, said the company has no energy exploration or production facilities, investments or employees in Sudan... A February letter on Berkshire's Web site deplores the situation in Darfur, while defending the PetroChina investment. A subsidiary isn't responsible for actions of the parent, and divestment would only help the Sudanese government get control of the Chinese assets inexpensively, the letter says.