An original experimental set-up was developed and used for studying crystallization and theology of methane hydrate/water/dodecane system. Methane is injected in a water in dodecane emulsion at low temperature and high pressure in order to form methane hydrate crystals and to move the suspension by gas lift. It behaves as a Newtonian fluid. Dynamic viscosity and conversion of water and gas into gas hydrate crystals were measured during the process for various water contents. Experimental results were explained by means of a model including nucleation, growth and agglomeration. Due to the high value of crystal and drop concentrations, agglomeration takes place through three-body collisions between one water drop and two already formed agglomerates. Resulting agglomerates were considered as fractal-like ones. During crystallization and agglomeration, the effective volume fraction of drops and porous agglomerates is increased, and then suspension viscosity increases. When all water drops are crystallized, agglomeration stops and viscosity does not change. (c) 2005 Elsevier Ltd. All tights reserved.