Equilibrium conditions for clathrate hydrates formed from methane and different concentrations of I-propanol or 2-propanol aqueous solutions were experimentally determined at temperatures of 274.0-287.1 K and pressures up to 11.0MPa. Each propanol has an inhibiting and/or promoting effect on hydrate formation depending on the propanol concentration. A structural transition from a structure I to a different hydrate structure occurred at concentrations between 3 and 5 mass% for 1-propanol and between 2 and 3 mass% for 2-propanol. (C) 2008 Elsevier B.V. All rights reserved.