Iran in September will send out invitations to energy companies to vet interest in the first contracts in the post-sanctions area, a director said Tuesday.

Iranian Oil Minister Bijan Zangeneh introduced revised terms of a new contract model for oil companies looking to re-enter the country after years of sanctions pressure. The terms should be finalized by the end of the year, though officials in Tehran have touted the opportunity as very flexible.

Ali Kardor, the managing director of the National Iranian Oil Co., said Tuesday foreign bidders were being called to the table.

"Next week, we will be sending invitations to foreign companies and ask them to announce if they are interested," he was quoted by Iran's Press TV as saying.

The first official tenders for oil field development are scheduled for late October with oil fields straddling the western border with Iraq among the early offers. According to Tehran, the border Azadegan complex holds around 6 billion barrels of recoverable oil reserves.

Two years ago, a contract with China National Petroleum Corp. for development of the South Azadegan oil field was torn up because the company wasn't meeting Iran's expectations.

Kardor said earlier this year that only those international companies that meet his company's standards would be eligible to play a role in Iran. Outside of companies with headquarters in the United States, he said there are at least 35 companies that may be eligible to take part in auctions.

Austrian energy company OMV was among the first to sign agreements with Iran in a step toward resuming formal operations in the oil-rich member of the Organization of Petroleum Exporting Countries.

Royal Dutch Shell paid off its debt to its Iranian counterparts early this year, clearing the way for the company to resume its cooperation with Iran now that sanctions pressures are easing. A shipment of Iranian crude oil was sold to Shell in June.