Effective oil for flushing is one that is high in mono-unsaturated and low in saturated. This ensures a high emulsification of the oil/acid potion, minimum time in the stomach and easy absorption in the body.
There are a few oils that fit this specification as can be seen from the table:
Another requirement is that the oil can be obtained from a cold pressing from fresh ingredients. Also that the resulting oil doesn't require chemicals to preserve of enhance the product. Many oils have a short shelf life. Some oils have caustic soda added to make them clear. These chemicals can be absorbed into the body undermining the benefits of the flush or in extreme cases case vomiting.
Most people think that by purchasing "extra virgin" olive oil they are getting high quality oil but a label reading extra virgin is no guarantee of quality. Extra virgin oil should have a free oleic acid acidity of no more than one percent, whereas ordinary virgin olive oil can have an acidity of up to 3.3 percent. Lower quality oils can be refined to bring the acidity down so they can be labelled as extra virgin. To complicate matters even more, the term "extra virgin" has no official meaning in the United States. Chemicals can be added to the olive to make it look clear and more appealing. For one thing, nowhere does it say that extra virgin olive oil has to be made 100% from olives. As much as 20% hazelnut oil can be added to olive oil by unscrupulous manufacturers and still be undetectable to the consumer.
Notwithstanding this advice it is possible to flush with other oils and many people use the usual cheap super markets brands. If you are sensitive then go for the better higher quality oils.