High pressure x-ray diffraction and electrical resistance measurements have been carried out on BaFe2 As2 to a pressure of 35 GPa and temperature of 10 K using a synchrotron source and designer diamond anvils. At ambient temperature, a phase transition from the tetragonal phase to a collapsed tetragonal (CT) phase is observed at 17 GPa under nonhydrostatic conditions as compared to 22 GPa under hydrostatic conditions. The superconducting transition temperature increases rapidly with pressure up to 34 K at 1 GPa and decreases gradually with a further increase in pressure. Our results suggest that T C falls below 10 K in the pressure range of 16-30 GPa, where CT phase is expected to be stable under high-pressure and low-temperature conditions. © 2010 The American Physical Society.