Some essential oils can last up to 3 years and should always be stored in dark colored glass containers. Most oils will last at least 1 year, except for citrus oils, which begin to lose their potency after 6 months. That is why it is a good idea to keep blank adhesive labels handy so you can write your purchase date on your essential oil bottles.
Do not make the rookie mistake of using the same eyedropper for all of your essential oils. Cross-contamination easily occurs because these oils are so volatile. Even a tiny amount of crossover can render an oil unauthentic. You should store your oils in a dry, cool environment that does not receive any direct sunlight.
Contrary to popular opinion, your eyedropper lids should not be screwed too tightly onto your oil bottles. Over-tightening shortens the lifespan of your essential oils. Tighten your lids firmly, but not overly so.
If you know you are not going to be using a particular oil for an extended period of time, use the original screw-on lid that came with that bottle. This keeps your oil from evaporating. Remember that mixing any oil with a carrier oil reduces the lifespan to 6 months, but only if refrigerated and securely capped.