(EnergyAsia, July 21) — US energy companies Chevron Corporation and Unocal Corporation have jointly announced an amended merger agreement, raising Chevron’s offer for Unocal from US$16.5 billion previously to US$17 billion. The announcement represents a rejection by the Unocal board of an US$18.5 billion offer from China’s state-owned CNOOC which has become the subject of…