We use x-ray computerized tomographic (CT) imaging to present quantitative aperture data for three-dimensional interconnected fracture networks imbedded in intact opaque rock samples several centimeters in length. X-ray images are obtained by injecting a high-density liquid metal into the fractured rock specimen under lithostatic conditions. The combination of tomographic reconstruction with gravimetric analysis makes it possible for the first time to obtain effective fracture aperture sizes to an accuracy of only several microns, located spatially within 300 microns. The apertures in the fracture network are spatially correlated over distances of 10 mm to 30 mm. The apertures of the intersections of the fractures were not found to be statistically larger in size than for the complete fracture network¿ 1997 American Geophysical Union