Avocado oil has risen in popularity in recent years because of its light, buttery flavor and numerous health benefits. But a study from the University of California warns a whopping 69 percent of avocado oils had impurities and cheaper oils mixed in. The study says many of the avocado oils tested had high levels of oxidation indicating the oils started to turn rancid. It didn't matter if consumers bought expensive avocado oils or low-cost brands.