How can ISIS, cut off from the rest of the world by financial and trade sanctions, and under daily aerial and land bombardment by some of the richest countries in the world, afford to maintain a well-armed military and pay other bills? The terrorist group relies on ... cash, crude oil and contraband. The ISIS economy and its fighters predominantly rely on the production and sale of seized energy assets - Iraq has the fifth-largest proven crude oil reserves in the world. ISIS also depends on the steady income it extracts from private donors, the heavy taxation and extortion it levies on its captive population, the seizure of bank accounts and private assets in the lands it occupies, ransoms from kidnappings and the plundering of antiquities excavated from ancient palaces and archaeological sites. Grossing as much as $40 million or more over the past two years, ISIS has accepted funding from government or private sources in the oil-rich nations of Saudi Arabia, Qatar and Kuwait - and a large network of private donors, including Persian Gulf royalty, businessmen and wealthy families. Only after widespread criticism ... did Saudi Arabia pass legislation in 2013 criminalizing financial support of terrorist organizations such as Al-Qaeda, Al-Nusra and ISIS. The lootings, ransoms and extortion ... provide a steady cash flow. But this is nothing compared to what oil trafficking provides.