The estimate indicates that Opec may be relaxing adherence to supply curbs, as oil prices hit a record of $90.07 a barrel on Friday, before falling to $85 on Wednesday.
The group on September 11 agreed to boost production starting from November.
Javad Yarjani, head of Opec affairs at Iran's oil ministry, said oil price rises were being fuelled by fear.
"The real reason for prices being so high is not the shortage of crude oil. Fundamentally there is no problem," Yarjani said.
"There is a fear factor, discussions of a political nature which are pushing up prices. We have to go back to the basics of the oil market, which is demand-supply, investments, flow of technology.
"It is mentioned that a piece of news about a dispute between Turkey and Iraq, which has increased prices by up to $8. That shows how fear is working."
Oil has risen by approximately 40 per cent since the beginning of this year, triggered by tighter supply and demand concerns ahead of winter months and amid political tensions in the Middle East.