The growth rates of methane (CH4) + propane (C3H8) structure II (sII) hydrates were measured via C-13 NMR in a custom-built nonspinning probe. The CH4 + C3H8 hydrate surface reaction growth data suggested that the large cages occupied by C3H8 formed twice as fast as small cages filled with CH4, although there were half as many large 5(12)6(4) cages as small 5(12) cages in a sII unit cell. Growth rates were measured at 269 K as a function of ice particle size ranging between 150 and 1180,mum, and vapor pressure in the range 0.34-0.84 MPa. A hypothesis based on low occupancy of sII small cages was presented to explain faster growth of large cages. A simple surface reaction model, which related growth rate to pressure and particle size, was developed.