According to today's headline data, jojoba oil in base oil has the longest preservation time. If it is produced by cold pressing, basically unopened 100% pure essential oils can be kept indefinitely for several years, such as sandalwood and olibanum oil, which are as mellow as alcohol.
For unsealed essential oils, attention should be paid to sealing as much as possible, which is easy to deteriorate when exposed to air; Citrus essential oils can't be preserved for a long time, but only for two years, except for bergamot. The storage period of essential oil blended with base oil is about two months. If you want to extend the shelf life, you can add 10% wheat germ oil to the blended oil, which can be extended to six months.