The authors consider the deadlock avoidance problem for a class of (sequential) resource allocation systems (RAS), which allows for multiple resource acquisitions and flexible routings. A new siphon-based characterization for the liveness of Petri nets modeling RAS is developed. This characterization facilitates the development of a deadlock avoidance policy that is appropriate for the considered RAS class. The resulting policy is characterized as C/D-RUN, since the starting point for the policy development was motivated by the RUN DAP, originally developed for sequential RAS with unit resource allocations and no routing flexibility. The last part of the paper exploits the aforementioned siphon-based characterization of RAS liveness in order to develop a sufficiency condition for RAS liveness that takes the form of a mixed integer programming formulation.