• BP Amoco, London, is forming a joint venture with PetroChina Corp., a unit of state-owned China National Petroleum Corp., to market gas in eastern China. BP Amoco purchased 20% of the shares in PetroChina's initial public offering last month. • Conoco, Houston, has acquired a 30% working interest through a farm-in on Block 15-2 in the shallow-water Cuu Long Basin, offshore Vietnam. The first phase in Block 15-2 is currently producing about 35,000 bbl. per day of oil from the Rang Dong Field. Conoco's current net production from the field is about 6,000 bbl. per day. • Greka Energy Corp., New York City, has repurchased its noncore Colombian assets from Omimex Resources Inc. for $12 million. Greka will give back to Omimex some California assets that it acquired from Omimex. -Heather H. Read