Iran has the second largest proved gas reserves in the world after Russia, with 33.6 trillion cubic metres, and third largest natural gas production in the world after Indonesia, and Russia. It also ranks fourth in oil reserves with an estimated 153,600,000,000 barrels. It is OPEC's 2nd largest oil exporter and is an energy superpower. In 2005, Iran spent US$4 billion on fuel imports, because of contraband and inefficient domestic use. Oil industry output averaged 4 million barrels per day (640,000 m3/d) in 2005, compared with the peak of six million barrels per day reached in 1974. In the early years of the 2000s (decade), industry infrastructure was increasingly inefficient because of technological lags. Few exploratory wells were drilled in 2005.