Ultrasonic attenuation spectra (1-150 MHz) of a series of 5 wt % oil-in-water emulsions containing hydrocarbon droplets (n-decane, n-dodecane, n-tetradecane, n-hexadecane, n-octadecane) stabilized by various surfactants (Brij 35, Tween 20, SDS, Triton X-100) were measured as a function of time. Droplet size distributions were calculated from attenuation spectra using ultrasonic scattering theory. Changes in droplet size distribution were also measured by static light scattering on the same emulsions after dilution (<0.01 wt %). Ostwald ripening rates were determined from the time-dependence of the mean droplet size using the Lifshitz-Slyozov-Wagner theory. Ultrasonic spectroscopy was more sensitive to small changes in droplet size than light scattering and could be used to analyze emulsions containing smaller droplets (d < 100 nm). Ripening rates decreased exponentially as the molar volume of hydrocarbon increased. They also depended on the type of surfactant used to stabilize the emulsions, decreasing in the following order: Brij 35 > Tween 20, Triton X-100 > SDS. The addition of excess surfactant (0.5-5 wt % Tween 20) to n-tetradecane emulsions stabilized by Tween 20 had little influence on ripening rates.