This work shows that hydrate formation in black oil systems can be incorrectly predicted for two major reasons: (1) a large degree of metastability associated with hydrate formation and dissociation and (2) a previously unconsidered effect of water cut on the water activity and hydrocarbon bubble-point. A new experimental technique is introduced to accurately assess the pressure-temperature equilibrium. A third and forth reason for prediction discrepancies, those of accurate oil characterization and hydrate structural change, awaits future assessment. (C) 2004 Elsevier B.V. All rights reserved.