Very few truffle oil offerings have anything artificial whatsoever. The Istria products are much cheaper than the Italian or French ones, usually, but are of generally equal quality, IMHO. We use them for salad dressings and drizzle some over pasta and other foods. They keep well if kept completely in the dark, closed and sealed. Once open none of them last, just as pure olive oil does not.

As several posters have commented the stuff is made by filtering olive oil through truffle pieces, often with a bit of steeping involved. I have never seen one that did not have extra virgin high quality oil.

There is much less difference between white and dark truffle oil than there is between the fresh truffles, but some of the truffles themselves are mislabeled. It is not rare to find cheap, tasteless truffles or truffle oil that repackages truffles from China or somewhere else, using oil from a good location, labeling the entire mess as from Italy or France. I have never heard of a fake from Istria, so we tend to seek the Istrian product because it is consistent.

Just in case you do not know, the truffles of Istria are the same as those from northeastern Italy because the conditions are similar. However, the Istrian product is often in better supply, so is les expensive. If you cannot find them in your area seek out anywhere there are Croatian foods or supplies and you'll probably find them. Otherwise wholesalers that carry Italian products from Trieste (think Illy coffee) often have truffle and olive oil from the region also, often sourced from Istria.