Energy consumption in any manufacturing has become of greater importance in recent years, particularly in energy intensive industries such as cement production. Any factors that can lower the energy consumption, and therefore the energy cost of an operation are carefully analyzed. This is especially true for certain areas of the cement industry, for example, import and distribution terminals. In light of the concern over energy usage, pack set has become an increasingly important test, particularly in the fields of bulk solids handling and pneumatic transport. This paper will deal with the latter topic, by first providing a description of the equipment, procedure and results of the pack set test as prescribed by the American Society of Testing and Materials. Factors affecting pack set are then discussed. Suspicions of pneumatic conveying capacity reduction due to pack set in several cement transfer systems led to the need for lab pneumatic conveying testing to provide preliminary information and direction for field testing. Results of this testing with and without a commonly used grinding aid (diethylene glycol) are summarized, followed by the description of practical experiences from several field installations that had experienced capacity shortfalls due to high pack set. This field experience and resolution of capacity issues validates the lab testing results, and provides full scale data for the analysis of the real operating costs of excessively high packset. A sample calculation is included showing the significance of this cost.