The dependence of the ultrasonic attenuation spectra (0.4-160 MHz) of n-hexadecane oil-in-water emulsions on droplet concentration (1-92 vol %) was measured. In dilute emulsions the attenuation coefficient increased with droplet concentration, but in concentrated emulsions it decreased. Traditional multiple scattering theory (Allegra and Hawley-Waterman and Truell) greatly overestimated the attenuation, even at moderate concentrations (>10%), because it ignores thermal overlap effects. On the other hand, an extended multiple scattering theory that takes these effects into account gives good agreement with experimental measurements up to much higher droplet concentrations (50-70%). Neither theory could be used to accurately predict the ultrasonic properties of highly concentrated emulsions (>90%).