A new energy decomposition method, called the Log-Mean Divisia Index Method I (LMDI I), is presented. It has the desirable properties of perfect decomposition and consistency in aggregation. Perfect decomposition ensures that the decomposition results obtained do not contain a residual term. Consistency in aggregation allows estimates for sub-groups to be aggregated in a consistent manner. The formulation of the new method and the usefulness of aggregation consistency in energy decomposition studies are described. Two case studies on energy-related CO2 emissions are presented.