The energy efficiency of comminution processes is very low based on the energy required to generate new fracture surface area relative to the mechanical (strain) energy input. However, the maximum ideal limiting efficiency ELimit against which actual efficiencies may be compared is unknown. Therefore, theoretical analyses were undertaken to determine ELimit for a compressive loading comminution machine based on the stress state in a single particle containing a central crack (flaw). The analyses show that ELimit increases with increasing Poisson’s ratio ν, having values of 5%, 7.5% and 9% at ν 0, 0.2 and 0.39, respectively. Actual energy efficiencies, EB, expressed in terms of the energy required to create new fracture surface area relative to the work input, using standard Bond work index values, are lower in the range <1% to 2%. The relative efficiency ratio EB/ELimit varies from 3% to 26%, depending on the mineral, and is considered to be a more useful (practical) measure of efficiency because it gives a better assessment of behaviour relative to the limiting situation. It is concluded from the EB/ELimit ratios that the potential exists to improve comminution efficiencies by two or three times. Possible methods of achieving this are discussed.