1. Geology and Geochemistry Research Division, IFP, 1-4 Avenue de Bois Préau, BP 311, 92506 Rueil-Malmaison Cedex, France
2. Shell International Expl. & Prod., 3737 Bellaire Blvd., Houston, Texas 77025
3. Chevron Research and Technology Co., Richmond, California 94802