As I see it, the cost of production turns largely on two main factors:
1. Character and quality of the geology/field/reservoir/reserves;
and
2. Efficiency/engineering/management skills of the operator.
then you add in:
3. Transpotation costs; and
4. Taxes.
You can have a brilliantly run company producing in a relatively difficult oil field that can’t match the dollar per barrel costs of Saudi Aramco. This is because the pressure, porosity, permeability, amount of oil in place, etc are simply that much better in Saudi than in most of our fields, especially the shale/tight fields.
Now you could have a bloated, inefficient, wasteful company (cough, cough PEMEX, cough, cough...) that has had some pretty good geology over the years, but is still, at times, more costly per barrel than much better run lean US producers operating with somewhat worse geology.