This article deals with the decomposition analysis of energy-related CO2 emissions in Greece and in the EU-25 from 1990 to 2020, by means of the Logarithmic Mean Divisia Index technique and a baseline scenario approach based on the PRIMES simulation modeling system for energy demand and supply. The Logarithmic Mean Divisia Index technique is used and changes in CO2 emissions are decomposed into four factors: income effect, energy intensity effect, fuel share effect, and population effect. For comparison reasons, we have included in our analysis results for three other countries (i.e., Ireland, Portugal, and Belgium) of similar size with Greece and varying energy mix and economy structure. Finally, a sectoral decomposition analysis of CO2 emissions for the Greek economy is applied.