Another One For Your Science Teachers [Possibly?] Make Glass Appear To Be Invisible
The only way this will work is if the refractive indices of the glass [to made to appear to disappear] and the oil have similar values.
Link 1: Refractive Index List of Substances - Table of Refraction Indices [Search for text: Glass, Pyrex]
Link 2: Index of Refraction of Vegetable Oil [Search for the following texts: Corn Oil, Vegetable]
It might surprise a few students when demonstrated to them live.
Edit: Sugar solution may also work: Search the first link for: Sugar Solution 80%