The composition and thermal properties of palm olein upon storage have been investigated by numerous techniques such as Differential Scanning Calorimetry (DSC), Gas Chromatography (GC) and High Performance Liquid Chromatography (HPLC). DSC melting and crystallization thermograms of crystals separated from palm olein differed in their characteristics, according to the composition of the olein and the storage conditions. A comparison was made between oleins of iodine value (IV) in the range of 56-61 which were stored at conditions of 20°C and 5°C. The more unsaturated olein was stored at 5ºC. Oleins with higher unsaturations showed crystals with a group of exotherms and endotherms which generally did not differ much with duration of storage. Crystals of the more saturated types of olein still retained the two exothermic and endothermic peaks, as observed in palm oil. The crystals of unsaturated oleins (IV of 60.6) tended to have a higher proportion of POO than POP, in contrast to the crystals of oleins (IV of 57.7) where the POP content is higher. With longer storage period, these exotherms and endotherms were shifted closer together, depicting polymorphism upon melting. With a long duration of storage, as in ambient storage conditions, another set of olein samples resulted in crystals with harder characteristics and a melting point of about 68°C. These crystals contained high diglycerides, confirming earlier works on the strong role of diglycerides in the crystallization stability of palm olein.