Iranian and Russian companies have signed a contract worth up to $1 billion to develop the Zagheh heavy oil field in south Iran, Iran\'s Petroleum Engineering and Development Company (PEDEC) said on its website. The deal between PEDEC, the subsidiary of the National Iranian Oil Company (NIOC), and Tatneft, one of Russia\'s top ten crude oil producers, was signed on Sunday. A statement by PEDEC says the deal is worth $1 billion, while Tehran Times puts the contract value at $700 million. According to Press TV, Iranian Oil Minister Rostam Qasemi declined to specify the contract value. \"The contract is still in preliminary stages and its technical details are not ready yet. We hope to be able to estimate and announce its value in two months,\" Press TV quoted the minister as saying. The deal was signed by Naji Sadoni, managing director of the Petroleum Engineering and Development Company and Rustam Minnikhanov, the leader of Tatarstan who also heads the Tatneft board of directors. \"By signing the contract, production capacity of the [Zagheh] oil field is set boost by seven thousand barrels per day in the first phase and 55 thousand barrels per day in the second phase,\" a PEDEC statement reads. Iran is the second largest oil exporter among the OPEC countries and holds the fourth place in the world by oil output. Oil exports account for about 80 percent of Iran\'s revenues.