We have observed the growth behavior of gas hydrate with addition of surfactants by several observation methods, and we discuss the mechanism of gas hydrate formation along the wall surface. From observation using colored water, the water moves up through the porous hydrate structure and unreacted water remains in the middle of the porous hydrate. In contrast to previous studies which observed growth from the side, we observed the growth behavior from the top. The hydrate height agrees well with that of water pulled up by capillary action. These results confirm that the driving force for hydrate growth in the vertical direction is capillary action. We discuss the driving force for hydrate growth in the horizontal direction. We suggest that the driving force in the horizontal direction is different because the initial concentration of the surfactant solution affects the growth behavior in the horizontal direction while it does not affect the hydrate height. (C) 2017 Elsevier B.V. All rights reserved.