The main energy absorbing mechanisms during quasi-static crush of a circular composite tube have been investigated using an axisymmetric finite element model. Failure mechanisms such as material failure, delamination, friction between plies and friction between a metallic initiator and the tube are explicitly represented in the model. A Design of Experiments (DOE) study is performed to estimate the contribution of each of these mechanisms on the total energy absorbed. The results confirmed that friction between the tube and the initiator was the dominant mechanism, representing approximately 50% of the total energy absorption. The delamination mechanism did not absorb significant amounts of energy, but the presence of delamination had a strong effect on the bending stiffness and the deformation of the tube, which in turn affected strongly the total energy absorbed. The results of this study not only provide a better understanding of tube crush behavior, but also guide the development of better models for design of composite crush tubes.