The eikonal equation of ray acoustics is discussed for the general case, with the index of refraction a function of the three space coordinates. Two examples illustrating the influences of a two‐dimensional heat source and a thermal‐mixing zone on the acoustic‐ray paths are presented. Numerical results show that, for long‐range acoustical ray tracing, inhomogeneities of the ocean in the horizontal plane can cause refraction effects, which are not negligible in comparison with effects due to vertical inhomogeneities. Rays, which travel in the vicinity of a heat source, can be refracted as much as 6°. Thermal‐mixing zones can increase the range of shadow zones near the ocean surface up to 50%. Even new shadow zones can be formed.