Specific energy is simply defined as the work done per unit volume of rock excavated. Specific energy is an important performance parameter as it relates cutting force to the amount of rock excavated. In this paper the development of a new rippability classification system for coal measure rock based on specific energy is presented. Extensive field and laboratory studies were conducted at six different lignite open pit mines and rock mechanics laboratory. Since both ground and machine properties are incorporated, the rippability classes of rocks and the approximate hourly ripper productions of different dozer types can be assessed by using the developed system. (C) 2008 ISTVS. Published by Elsevier Ltd. All rights reserved.