Some empirical relations between diffusion characteristics are investigated by the use of carefully examined data from dye release experiments in the surface layer of the sea. These data cover a time scale of diffusion ranging from 1 hour to 1 month and a length scale from 100 m to 100 km. Two 'oceanic diffusion diagrams' are prepared; one showing horizontal variance versus diffusion time and the other showing apparent diffusivity versus the scale of diffusion. The overall behaviors of the horizontal variance and of the apparent diffusivity are evidently different from those which the similarity theory of turbulence deduces. However, there still remains a possibility that the similarity theory may be valid locally in time- or length-scale with a variable parameter, i.e., the rate of turbulent energy transfer. The diagrams provide a practical means to predict the rate of horizontal spread of substance introduced from an instantaneous point-source as well as the apparent diffusivity as a function of the size of diffusing patch.