India has offered to invest up to 20 billion US dollars in Iran's energy industry, subject to provision of concessional rights.Oil Minister Dharmendra Pradhan, who is in Iran with a delegation of state-owned companies informed the Iranian side that Indian companies are interested in setting up petrochemical and fertiliser plants, including those in Chabahar SEZ. He also requested them for favourable treatment in the pricing of gas and supply of rich gas at competitive price on long-term basis, an official statement said.On payment of dues by Indian refineries,Mr.Pradhan conveyed that India is committed towards making payments as and when banking channels, acceptable to both sides, are available.The two nations, also discussed developments regarding Farzad-B gas field and expressed confidence in concluding an agreement at the earliest,the statement added. This was the first visit by an Indian minister since the US and other western powers lifted sanctions against Iran in January.