Answer :

Gibbs
Iran's primary natural resource export is petroleum products. Petroleum products include both oil, natural gas, and others. Therefore, out of this list the best answer is oil. 
francocanacari

Iran's primary natural resource export is oil.

The majority of Iranian exports and government revenues are oil and natural gas. In 2010 they accounted for 80% of foreign exchange earnings -permitting to reach reserves of more than 80,000 million dollars in March of that year- and 60% of the total budget of the state.