The world's largest company by market capitalization is the Chinese energy company PetroChina. The Financial Times's Lex column reports that PetroChina's Chinese-government-owned parent company, CNPC, just spent about $600 million to buy back about half a billion PetroChina shares, raising its ownership stake to 86.54% from 86.29%. "The best explanation is a creeping re-nationalisation of the state's most prized strategic assets," the FT says. There's both a Goldman Sachs angle and a Warren Buffett angle on PetroChina. At least here in America, the government says it wants to eventually exit its positions in companies such as General Motors and Citigroup. No such luck in China.