nowhere, I personally believe that tax can go as low as 0, if the oilprice keeps dropping. Simply to keep the production going. Again, it is a national security Q, too important to let in the hands of the Sauds and other 3. world countries.
The oil companys have an interest in stating that the production
pr. barrel is high, when (re)negotiating with the state, to put a pressure on for a low tax. That is why it is not possible to get an excact figure. The only thing for sure is, when there is no money in it, then the operators are out - which is the fact for most US fracking companies.
Enough said on this subject....