In this report, ESCWA developed a hybrid general equilibrium model with overlapping generations taking  into account the heterogeneity of the agents and the non-linearity of pension formulas. The model used Tunisia as a case study to assess the viability of the pension system and ways for pension reforms. The first part of the paper presents the  theoretical structure of the model. The second part presents the demographic and legislative context of the Tunisian pension system. The third part of the paper presents the model results and provides an assessment of some standard reforms for Tunisia. The forth part of the paper presents the user manual of the interface developed for this model and its results and finally the paper concludes with a number of inferences and suggestions.