How Big Oil avoids billions in taxes?

I believe that special interest groups - the most well funded - always get whatever "tax breaks" their money will buy. I also believe that capitalistic greed is based on creating shortages of commodities & resources so that the prices must go up whether the shortages are real or created. I would guess that over this past century most people do not realize our government regulations have been erode to allow the monopolies to once again avoid the scrutiny & protection that was in place since the 1920s to protect the general public for the monied interest of big oil, telephone & utilities corporate entities. I think we are paying the price now for that lack of interest in our own history.