In a nod to the Saudis, he said he hoped Opec members understand that "when a member country comes back ... they should open the doors for him and not fight with him".
Many oil companies are eager to get back into Iran, and Zanganeh said he had meetings set up with some while in Vienna. He gave no details, saying, "many eyes are watching us and working against us".
Saudi Arabia might be hard to persuade. It produces close to a third of the daily 30 million barrels Opec accounts for.
Bitter regional rivals with Iran, the Saudis may not be ready to cede much ground. And with their producing clout they usually make Opec policy.
The Saudis already set the meeting's direction even before it convened. Riyadh is happy with present prices well above US$100 a barrel for the internationally traded benchmark crude and comments by Saudi Oil Minister Ali Naimi suggested the group would keep the overall production target.
"We are at the right price right now," he said.
Beside the gap left by Iran sanctions, Libyan output is strongly down because of unrest. That leaves a production hole that the Saudis are happy to fill.
"The continuous output issues in Libya ... coupled with the Iran sanctions, leaves the Saudi spigot in firm control," said the Kilduff Report, edited by Michael Fitzpatrick.
That could change next year, though, if production from Iran and Libya comes back and Iraq's remains strong - it already puts out about 3 million barrels a day. That, and strong US shale oil production, will likely increase internal competition, as the three countries jostle for Opec share. Political tensions could also grow, with Sunni Saudi Arabia vying with Shiite-led Iran and Iraq.
"Not only do they have to deal with rising US production, they have to deal with the fact that they hate each other," said oil analyst Phil Flynn of the Saudis and Iranians.
All three countries have put forward candidates for Opec secretary general. But with their rivalries strong and potentially harmful to Opec unity, the meeting could skirt the issue and extend Libya's Abdullah Al-Badry's term for another year.
- AP