All foreign taxes paid by US corporations including oil companies are deducted as credits from US taxes payable, dollar for dollar. The "royalties" paid by US oil companies were (during my working years) considered taxes by IRS and were therefore deducted from US taxes payable.
PING! to #17
It was my understanding that during the reign of the Sha, Kissinger suggested to him that he raise the royalties on oil in order to help Iran to pay for arms from the US. Kissinger's thought was that since these would be deductible by the oil companies, their relationship with the administration would not be hurt, the arms industries would get a boost, the Sha would get his arms and the only one to get hurt would be the US drivers.
Another question, when OPEC raises the price/bbl, are they raising the actual price, or are they raising the royalties (much as a 'severance tax')?