The “introduction of oil from Iran” is overblown as a factor here. The U.S. embargo against Iran altered the way oil was traded on the global markets, but it didn’t stop Iran from selling oil. I believe they were the fourth-largest oil producer in the world even with the embargo in place.
They are down to 7th place in 2014.
http://www.eia.gov/beta/international/rankings/#?prodact=53-1&cy=2014&pid=57&tl_id=1-M&tl_type=a