A model has been developed that can predict the three-dimensional motion of a fiber as it is being formed below a melt-blowing die. The model involves the simultaneous solution of the momentum, energy, and continuity equations. The model equations are solved numerically with both Newtonian and viscoelastic constitutive equations. Predicted parameters include fiber attenuation, vibration frequency, vibration amplitude, temperature, and stress. The predicted results compare favorably with previously published experimental data.