Using one-group diffusion theory, linear extrapolation distances for centrally and eccentrically located black control rods in cylindrical geometries have been determined by the pulsed neutron method. It is found that for a given radius control rod, the extrapolation distance increases with increasing moderator radius. Linear extrapolation distance is also found to increase with eccentrical location of control rods. In general, the values of the extrapolation distances determined for central rods in diffusion theory, in the range of moderator radii studied, are higher in value by 10 to 100% than the classical values based on the theoretical calculations of Davison and Zaretsky. The values of the linear extrapolation distances for eccentric control rods, in the range of the moderator radii studied, are also higher than the central control rod extrapolation distances up to a factor of 6, the increase depending on the location of the control rods.