In this paper the energetics of steady-state flows in coronal loops are examined as an example of flows in flux tubes. The equations of continuity, momentum, energy and state are solved numerically (with some analytical special cases) subject to prescribed temperatures and pressures at the footpoints. A large range of subsonic and supersonic solutions is found, and it is pointed out that the static solutions discussed previously in the literature are just one of a large family of more general dynamic solutions. A steady flow is found to remove the symmetry present in static loops and to lower the maximum loop temperature. Also, the possibility of acatastrophe, which can exist in static loops asnon-equilibrium, is found to be enhanced by the presence of a flow; it implies that for certain pressure and temperature differences between the footpoints, a hot (>106K) steady flow is impossible, and so either a cool (<105K) steady flow or an unsteady flow ensues. If the footpoint density is lowered, the threshold for catastrophe is raised.