The initial thickness of methane hydrate film was directly measured by suspending a single methane bubble in water at 274.0, 276.0, and 278.0 K. The results show that the initial hydrate film thickness decreases from tens of micrometers to about 10 mu m with the subcooling increased from 0.5 K to about 3 K. When subcooling is higher than 1.0 K, all initial film thickness data measured under different temperatures vary inversely with the subcooling. Notable three-dimensional growths of hydrate crystals of different sizes and shapes at film front and emergence of new crystal were clearly observed at lower subcooling that resulting in the rougher surface of hydrate film and uncertainty of initial thickness measurement under lower subcooling. The hydrate film growth was dominated by film growth in thickness, not by lateral growth at low subcooling. The growth in thickness of hydrate shell covering one whole bubble surface was also investigated. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 21452154, 2013