Two-dimensional gravitational spectra are derived from simple harmonic analysis of range rate tracking data on planetary orbiters. The eccentricity of the orbit is arbitrary, and results are shown to vary substantially with the aspect angle of the tracking line of sight with the orbit plane. The development for arbitrary start and stop times (with respect to periapsis) uses modified eccentricity functions evaluated by quadrature. Simulations with a point-masses model of Venus using tracking data on the Pioneer Venus orbiter show excellent predictions of the average orbiter spectrum over 1 Venus day. The Venus gravitational signal should be above the tracking noise level for arc lengths longer than 40¿ (in true anomaly) about periapsis and for terms as high as 55th degree. Analysis has been made of tracking residuals from a short-arc fit to Mariner Mars 9 data over the Hellas Basin (using a complete sixth-degree field). Results are most consistent with higher residual gravitational power than predicted from Kaula's rule for Mars.