Herring oils produced from three different types of byproducts, only heads, mixed, and headless byproducts, were compared. Heads byproducts and its oil presented the highest oxidation levels and the lowest alpha-tocopherol content. Heads contained the lowest polyunsaturated fatty acids content and the highest amount of saturated fatty acids. No significant differences were found between the fatty acid composition of the mixed and the headless either in byproducts or in its oil. The oil was stored at two different temperatures (20 and 50 degrees C). Testing general linear models showed that oxidation was related to the peroxide value with a positive significant effect of the temperature, while the free fatty acids' model was more complex, with significant contribution of all of the effects studied. Fluorescence measurement was the one that correlated best with the oxidation progress.