Mangalore Refinery and Petrochemicals Ltd (MRPL) will pay USD 300 million and a similar tranche may follow next month. Essar Oil will clear a little over USD 300 million in dues on September 30, top sources said.
HPCL-Mittal Energy Ltd (HMEL) and Hindustan Petroleum Corp Ltd (HPCL) will be the other refiners to clear their part of the outstanding on Wednesday.
Sources said the refiners will deposit rupee equivalent of USD 700 million in Kolkata-based UCO Bank which will then transmit the money to Reserve Bank of India (RBI).
Indian refiners owe over USD 6.5 billion in past oil dues to Iran and payments are being made in a calibrated manner so that there is no pressure on exchange rate, the source said.
US Treasury's Office of Foreign Assets Control last month approved Indian refineries paying USD 1.4 billion out of the USD 6.5 billion in past oil dues to Iran.
No modalities of the second installment of USD 700 million have yet been worked out, the source said.
The remaining USD 4 billion would be cleared in tranches after payment channels are cleared.
Sanctions will be lifted after the International Atomic Energy Agency verifies that Iran has implemented its commitments to cease nuclear programme.
Until then, the interim sanctions relief format of November 2013 would continue.
The dues to Iran on crude oil that refiners buy have accumulated as Western sanctions blocked payment routes since 2013.
About 45 per cent of the oil import bill is paid in rupees in a UCO Bank branch and the rest has accumulated.
The remaining has been accumulating, pending finalisation of a payment route and mechanism. They had last year paid nearly USD 3 billion in six installments through a limited payment channel following start of nuclear talks between the Western world and Iran.
The outstanding has since climbed to over USD 6.5 billion.
Essar Oil owes USD 3.34 billion, MRPL (USD 2.49 billion) and Indian Oil Corp (USD 581 million) to Iran. HMEL owes USD 97 million and HPCL another USD 29 million.