Using water or acetone as the working fluid, the thermal performance of a three-dimensional flat-plate oscillating heat pipe (3D FP-OHP) with staggered microchannels was experimentally investigated by varying heating area, cooling temperature and operating orientation. It was found that when the heating area is larger at the same input power, the heat pipe is less orientation-dependent. When the heating area was decreased, to form a localized heating condition and higher heat flux, the thermal resistance and peak-to-peak amplitudes of temperature oscillations in the evaporator increased. The utilization of water as the working fluid generally provided the lowest thermal resistance for all experimental conditions investigated, but - unlike acetone -resulted in more severe temperature fluctuations in the evaporator during localized heating. The 3D FP-OHP, with overall dimensions of 130.18 x 38.10 x 2.86 mm(3), demonstrated to efficiently manage heat fluxes as high as approximately 300 W/cm(2) at a total heat load of 300 W. (C) 2011 Elsevier Ltd. All rights reserved.