The remaining value can be attributed to oil and gas trading and energy products like natural gas, synthetic oil, bitumen and fuel oil.

FORBES: Connect

The US sanctions aim to stop international companies from investing in Iran's oil and gas industries or supplying it with petroleum products by preventing them from trading in the US if they trade with Iran.

BBC: Total stops petrol sales to Iran

The idea was that these exchanges would be able to trade products that are less susceptible to manipulation (as trading commodities like silver and oil are) between institutions that are seeking to hedge risks.

FORBES: Magazine Article