Differential scanning calorimetry has been used to monitor the crystallization of hydrocarbons in oil-in-water emulsions containing a mixture of pure (n)-hexadecane droplets ( (10 \mathrm{wt} %) ) and pure octadecane droplets ( (10 \mathrm{wt} %) ) stabilized by either whey protein isolate or casein ((0.5 \mathrm{wt} %)). The phase behavior of the emulsions changed with time in a manner consistent with oil exchange between the (n)-hexadecane and octadecane droplets. The rate of exchange was faster for the emulsion containing whey protein isolate than the one containing casein, and increased for both emulsions when additional protein ( (2.5 \mathrm{wt} %) ) was added to the aqueous phase. The addition of (\mathrm{NaCl}) ( 2.5 (w t %)) to the aqueous phase slightly decreased the rate of oil exchange. Measurements of the droplet size distribution of the emulsions during the course of the experiments indicated that the oil exchange was not caused by droplet aggregation or Ostwald ripening. We propose that the mechanism for oil exchange is the reversible binding of hydrocarbons to protein molecules (either at a specific binding site or by incorporation into micelles), and their subsequent transport through the aqueous phase separating the droplets. 1993 Academic Press, Inc.