Abstarct: Formation of gas hydrate is a serious problem in some offshore drilling in special conditions. Occurrence of high pressure in presence of low temperature, which occurs in sediments near the sea bed in deep sea, provides suitable condition for formation of gas hydrate. Formation of gas hydrate not only occurs in the mentioned geological condition, but also comes into happen in drilling facilities in deep sea drilling, such as pipelines; blow out preventers (BOP) and around drill string. This phenomenon will result in reduction of well pressure, blockages of drill pipes and space between drill string and formation and also affect performance of BOP valves. These problems all are serious risks in drilling operations. Therefore, it is required to perform some operations to prevent formation of gas hydrates in while drilling in deep sea. In this study, different gas hydrate prevention techniques were investigated to define the best technique and strategy for a special case of using water baxsed mud and some special preventers, in the presence of common chemical additives into the drilling fluid. This study was carried out by performing several experiments using different drilling fluids and various additives. In these experiments, I have used mixture of water and bentonite with different solid particles concentrations. Performance of bentonite in preventing gas hydrate formation was first tested in appropriate thermodynamic conditions. It was detected that the bentonite does not paly as a gas hydrate preventer. Subsequently, three different inhibitors, Na-Cl, Ca-Cl2 and mono-ethylene Glycol (MEG) in distilled water were tested separately in in mixture of them. As result, MEG performs as a suitable inhibitor in distilled water. To investigate effect of bentonite in preventing of gas hydrate formation in the presence of MEG, solution of water- Bentonite in two different concentrations was further tested. Finally, it was observed that the presence of bentonite dosent have changes in thermodynamic conditions of gas hydrate formation and also preventing of MEG, while Na-Cl and Ca-Cl2 exhibited acceptable performance as an inhibitor. The more the Na-cl and Ca-Cl2, the more preventing effect in the final drilling fluid.