We report, for the first time, bandgap guidance above 3 µm in a silica based air-core photonic crystal fiber. The peak of the bandgap is at 3.14µm with a typical attenuation of ~ 2.6 dB m-1. By further optimization of the structure, modeling suggests that a loss below 1 dB m -1 should be achievable, greatly extending the useful operating range of silica-based single-mode fibers. Such fibers have many potential applications in the mid-IR, offering an alternative to fluoride, tellurite or chalcogenide glass based optical fibers for chemical and biological sensing applications. © 2005 Optical Society of America.