In this paper we describe a new experimental set-up which makes possible the in situ determination of the particle size distribution of methane hydrate during its formation in a pressurized reactor. It has been installed on two research sites: one at the Institut Français du Pétrole (IFP) and the other at the Ecole des Mines de Saint-Etienne (EMSE). Thanks to this apparatus, new data can be obtained, in particular concerning the granular aspects of the crystallization processes and the reproducibility of the results. Particularly, we propose a new experimental procedure which allows us two important improvements: • a better reproducibility of the induction time, • the possibility of doing a large number of experiments in a day (around fifteen). Using this protocol, the effect of some kinetic inhibitors of the crystallization processes are shown: increase of the induction time and/or decrease of the quantity of hydrate formed.