The combined panel data matrix set consists of a time series for each cross-sectional member in the data set, and offers a variety of estimation methods. The present study aims to compare the estimates of different panel data estimation techniques by taking the example of Environmental Kuznets Curve (EKC). EKC is a hypothesized relationship between environmental pollutants and output. Plethora of research is available to determining relationship between environmental degradation and output. However in literature it is evident that when we change the assumptions of estimation technique, coefficients also get changed (Stern 2003). Therefore; it is important to reinvestigate the EKC using several panel data techniques. The primary objective of this study is to estimate the heterogeneous parameters and finding the cross sectional dependence of the large sample panel data. For the purpose we will not only rely on conventional panel data techniques but will also use 2nd generation test of cointegration. We hope to have clarified how to interpret the fact that the EKC hypothesis does not hold for individual countries, but emerges from the overall picture. Since the existing literature; except few assumed slope homogeneity and cross sectional independence so we expect that our study will contribute in the field of applied econometrics by reassessing the relationship between environmental degradation and output growth in a large panel data for three different groups of countries i.e. low income countries, middle income countries and high income countries. Further presence of structural breaks is also a phenomenon which cannot be ignored in presence of long panel data. Therefore; we have also assumed it to get a clear picture.After establishing a long run relationship we have applied Mean Group (MG), Pooled Mean Group (PMG) and Common Correlated Effect Mean Group (CCEMG) to measure the magnitude of the relationship among CO2 and output. The results confirm the presence of inverted U shape relationship between environmental pollution and output. However; the coefficients obtained by these techniques significantly differ from each other. Supervisor:-Dr. Abdul Jalil