Measurements of water flow through a sinusoidal fracture were undertaken to compare sinusoidal flow with parallel plate flow. Flow rates were measured through a fracture with an amplitude of 1.02 mm and a wavelength of 5.08 mm, with vertical separation ranging from 0.21 mm to 0.71 mm, and for Reynolds numbers (Re) ranging from 0.05 to 58. In addition, a series of lattice gas automata flow simulations of water flow through a sinusoidal fracture with the same dimensions were performed. Results from both the experiments and the numerical simulations reflect that, compared to a parallel plate channel, a sinusoidal channel has a significantly lower ability to transmit fluid. This is proposed to be due to the variation in the aperture measured normal to the flow path, the tortuosity of the flow path, and potential instabilities within the flow field. ¿ 1998 American Geophysical Union