Oil reserves in Iran, according to its government, rank third largest in the world at approximately 150 billion barrels (24×10^⁹ m³) as of 2007, although it ranks second if Canadian reserves of unconventional oil are excluded. This is roughly 10% of the world's total proven petroleum reserves. Iran is the world's fourth largest oil producer and is OPEC's second-largest producer after Saudi Arabia. As of 2009 it was producing an estimated 4.172 million barrels per day (663.3×10^³ m³/d) of crude oil. At 2006 rates of production, Iran's oil reserves would last 98 years if no new oil was found.

Iran has more than a century of history in exploration and production activities; the first successful exploration well was Masjid Suleiman-1 on May 26, 1908. Since then, based on the latest oil and gas reports, 145 hydrocarbon fields and 297 oil and gas reservoirs have been discovered in Iran, with many fields having multiple pay zones. A total of 102 fields are oil and the remaining 43 are gas, and there are 205 oil reservoirs and 92 natural gas reservoirs. According to Iran Energy Balance Sheet (2009, in Persian), 78 of these fields are currently active, with 62 onshore and 16 offshore, leaving 67 fields inactive at present. Some 23 hydrocarbon fields lie in border areas and are shared between Iran and adjacent countries, including Kuwait, Iraq, Qatar, Bahrain, UAE, Saudi Arabia and Turkmenistan .

Tehran ( pronunciation (help·info)) (Persian: تهران‎ Tehrān; pronounced [tehˈɾɒːn]), sometimes spelled Teheran, is the capital of Iran and Tehran Province. With an estimated population of 8,429,807; it is also Iran's largest urban area and city, the largest city in Western Asia, one of the largest in Southern Asia, and the 19th-largest city globally.

In the 20th century, Tehran was subject to mass-migration of people from all around Iran. The city is home to many historic mosques, churches, synagogues and Zoroastrian fire temples. Contemporary Tehran is a modern city featuring many structures, of which the Azadi (Freedom) Tower and the Milad Tower have come to be symbols of Tehran itself. In 2008 Tehran was the least expensive capital in the world and the second-least expensive city globally based on the cost-of-living index presenting the best value for money in the world. Globally it stands 19th by city population, 56th by the size of its GDP and 29th by the population of its metropolitan area. Throughout Iran's history, the capital city has been relocated many times, with Tehran being the 32nd national capital of Iran. Persian is the city's native tongue, with roughly 98% of the population able to speak and understand it. The majority of people in Tehran identify themselves as Persians. In pre-Islamic and early Islamic times, Tehran was called Ray (which in the Avesta occurs in the form of Ragha)^{[citation needed]}.