Rock fractures play a fundamental role in fluid migration through the crust, rendering them important in geoenergy applications. Although often modelled as smooth parallel plates, fracture surfaces are rough, and roughness impacts transport properties. Despite their importance, there remains a paucity of data related to what controls fracture roughness and, consequently, how this affects fluid flow. Here, we examine how fracture orientation affects fracture roughness in Nash Point Shale, using laboratory-and synchrotron-based µ-CT, and optical microscopy methods, and consequently how fracture orientation and roughness affect fluid flow through a series of core flooding experiments. We show that there is a strong correlation between fracture orientation, fracture roughness and surface area, for fractures between the Short-transverse and Arrester orientations. Fractures in the Divider orientation have both a larger surface area and higher roughness than fractures in all other orientations, which we relate to fundamental differences in the fracture mechanics in this orientation. We also measured the permeability of samples containing mated fractures of different orientations to bedding but discovered no systematic differences between them.