Due to the optically thin nature of the white light emission, all measurements of the energetics and dynamics of a CME are based on sky-plane projected quantities. The extent and distribution of the CME material along the line of sight is unknown. Thus, CME measurements have an inherent degree of uncertainty. In this paper, I identify the various (possible) sources of errors associated with measurements of CME mass and energy (e.g., instrumental, random, projections effects, etc) and give an error budget for the final measurements. I apply these errors to the statistics of mass and energy for several thousand CMEs observed with LASCO in 1996-2003.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html