Most E-Liquids will contain a combination of Propylene Glycol (PG, Vegetable Glycerine (VG), Nicotine & Flavouring.
Majority of E-liquids work on a balance between both Propylene Glycol (PG, Vegetable Glycerine (VG). But in some cases E-Liquid manufacturers produce E-Liquids which are 100% VG.