And, they calculate that the marginal effective tax rate on investment by a U.S. firm in a low-tax country is, remarkably, a negative 24 percent.

FORBES: A New Way To Address The International Tax Mess For U.S. Companies

During recent auctions in Alberta, Canada, and in Angola, the firm's know-how helped it secure the best fields, while rivals overpaid for marginal ones.

ECONOMIST: Oil