A two-step hydrate formation mechanism is proposed for gas hydrate formation: (1) a quasi-chemical reaction process to form basic hydrate and (2) an adsorption process of smaller gas molecules in the Linked cavities of basic hydrate. Based on the new concepts introduced in a previous article and the two kinds of equilibrium: the quasi-chemical reaction equilibrium of step 1 and the physical adsorption equilibrium of step 2, a simpler hydrate model has been developed. Extensive test results indicate that the new model is adequate for predicting the hydrate formation conditions for pure gases and gas mixtures.