The paper presents a simple and robust approach for calculating frequency-dependent rays in three-dimensional media. The proposed ray tracing procedure simulates propagation of locally plane fragment of a wave front. Ray properties depend on velocity distribution in some sub-volume around the ray and on wavelength at each point. We provide a numerical comparison of "fat" rays approach with the "exact" Helmholtz solver using complex 3D SEG salt model. This comparison show promise of using the concept of "fat" rays in 3D seismic data processing, i.e. comparison show that "fat" rays approach needs up to several orders less resources than Helmholtz solver, while the error between "fat" rays wave filed and "exact" solution does not exceed several percent.