The Irvingia gabonensis kernels, which have been extensively studied for their numerous virtues, including the ability to act against the accumulation of fats in the body [1], contain an oil. The aging of this oil under two different conditions of conservation was the subject of our work. One of the results was an increase in the content of long-chain carbonaceous fatty acids during aging for 11 months of storage at low temperature (6˚C) and at 30˚C. This behavior does not find a concordant explanation by the comparative analysis of the chemical indices. Hence, there is the need to use the Medium Infra-Red spectroscopy (MIR) which allowed to clarify the information of the saponification index, to justify the weakness of the formation of peroxides in the case of the conservation at 30˚C and to confirm the information given by the peroxide index. It also allowed to understand the formation of the long carbon chains by the "cis-trans" isomerization and the homolytic cuts which intervene within the matrix of the fat by the analysis of the number of −CH 2 and −CH 3 groups in the two conditions of conservation. This study reveals that the rapid solidification of Irvingia gabonensis oil at room temperature [2] is an advantage for its preservation at room temperature but a great weakness when the fat is stored at low temperature.