Disclosed are improved pharmaceutical formulations for the delivery of RNA interference agents, such as antisense RNA, micro-RNA and siRNA. The formulations employ mixed micelles including amphipathic conjugates of the iRNA agents and amphipathic micelle-forming molecules with extended hydrophilic chains. Also disclosed are methods of using the pharmaceutical formulations to increase delivery of an iRNA agent to an intracellular target, and to decrease extracellular nuclease degradation of an iRNA agent in the formulations.