After years of negotiation, China and the U.S. oil company Arco have reached an agreement in principle on developing a major natural gas field in the South China Sea, officials said Tuesday.

The agreement, between the China National Offshore Oil Co. and Atlantic Richfield Co. of Los Angeles, is expected to be signed Wednesday, spokesmen said.The accord will open development of the Yacheng 13-1 gas field in the Yinggehai Basin, south of China's Hainan Island in the South China Sea. The field has reserves of at least 100 billion cubic meters.

Arco China Inc. discovered the gas field in 1983, but negotiations on developing it have been held up by disagreements over pricing and on how the gas is to be marketed.