Diffusion of innovations models formulates an attempt to study the behavior of agents in the complex network structure, contagion of information and the related consequences. Pioneering approach by F. Bass (1969) is further developed with numerous research works. Later, considerations bring to the introduction of heterogeneity effect and marketing mix variables to the models.Empirical results show that the basic Bass model and its generalizations (GBM) can be studied as a modified form of the basic Logistic model. Recent work by Bemmaor(1994) explains the diffusion dynamics as a mixture of probability distributions obtained from individual level heterogeneity. In this presentation, we will make a short introduction to the diffusion models and also discuss a special heterogeneous agent based diffusion modelling at the aggregate level. Examples also given to explain the natural gas production and their reserves estimates in South Asian countries in terms of the technological diffusion of innovation.