A big consideration is the intensity or concentration of fragrance in the bottle. The concentration affects the price and sillage. Most fragrances are diluted with alcohol to prevent skin irritation and provide lift. Pure parfum is the most concentrated at about 30% oil. Eau de Parfum is more common and concentrated at 15-25% oil. Eau de Toilete is at 5-15% oil. Eau de Cologne runs about 2-4% oil. An unusual fragrance that is not encountered often yet is making a comeback is Eau Fraiche which uses water which results in a 1-2% oil.