They aren't oils.
They look like an oil, they act like an oil...
But oils (and fats/butters) are made up of different fatty acids. Fatty acids are what makes an oil an oil. Essential oils contain no fatty acids and therefore are not actual oils.
They are neither saturated or unsaturated.
So what are essential oils?
They are the extract of a plant. The “essential” in their name refers to the fact that the oil contains the essence of a plant, its fragrance.
Personally, I'm not a big fan of essential oils in skincare, but I sure love smelling them! My favorite is rose...what's your favorite essential oil?