Nonspecular reflection, which occurs when an incident beam is phase matched to a leaky wave, is an important tool for fluid-solid interface diagnostics. A recently developed complex ray analysis for modeling nonspecular reflection of two-dimensional Gaussian sheet beams [1,2] is here extended to account for rotationally symmetric three-dimensional (3D) Gaussian beams (GBs) with arbitrary collimation. As in our 2D analysis, we utilize the complex-source-point (CSP) technique by which a conventional point-source-excited field can be converted into a 3D quasi-Gaussian beam field by displacing a real point source to a complex location [3]. When the CSP field excited in the fluid interacts with a plane or cylindrically layered elastic medium, the resulting internal and external fields can be expressed rigorously in terms of wavenumber spectral integrals that are approximated explicitly by high-frequency uniform asymptotics [4]. The resulting expressions for the reflected field contain interacting specularly reflected beam and leaky wave contributions which establish the physical basis for the observed phenomena.