An industrial production of prefried french fries using palm oil as a frying medium was studied over a period of 12 days. Samples of oils and french fries were withdrawn once a day. The quality of both the oil and the french fries was assessed using two types of tests. Some tests, such as the determination of free fatty acid (FFA) and the determination of thiobarbituric acid value (TBA), oxifritest and Food Oil Sensor correspond to what was used by a quality control laboratory. More elaborate techniques such as the determination of polar components, polymers and cyclic fatty acid monomers (CFAM) were also used. Only small increases of FFA, TBA, polar components and polymers were observed. However, in the case of palm oil, which contains a high percentage of diglycerides, it is more reliable to determine the quality of the oil using the amount of polymers instead of polar components which may include some diglycerides. Thus a high "polar components" value (up to 20–25%) would not necessarily reflect an altered sample. The maximum amount of CFAM detected was 0.1% and they did not seem to be preferentially adsorbed on the french fries. These results, along with the sensory evaluations, showed that the french fries obtained in these production conditions were of good quality as far as the fat was concerned.