In a case study from Malaysia, horizontal stress magnitudes and third-order elastic constants were determined using full-waveform borehole acoustic waves along with the effective vertical stress and an acoustoelastic model based on nonlinear elasticity. When all three stress magnitudes and the stress-sensitivity coefficients of the zone of interest are known, the in situ calibrated velocity-to-stress transforms can be used to understand the effects of the stress path on velocities and could be used for time-lapse seismic and reservoir-geomechanics simulations.