Oil prices have dropped more than 50 per cent from July's record of $147.27 and expectations have grown that a global recession will further reduce demand.
Last week US crude was trading at around $72 a barrel.
Earlier on Saturday, Khelil was quoted in the Algerian El Watan newspaper as saying that Opec saw oil prices bottoming at $70-$90 per barrel.
"Normally, Opec has no price target. The market decides on prices. But people say that the bottom price, the bottom cost below which we can not step down, is between $70 and $90 per barrel," he said.
The oil ministers of Qatar and Iran have also said that a balance between supply and demand must be found so that the oil price does not slip further.
"We are targeting a fair price," Abdullah al-Attiyah, Qatar's oil minister, said.
"In my personal opinion, we are talking about a target price today not more than $100 or $120, but between $80 and $90 as a benchmark within which prices could oscillate and be acceptable to consumers and producers at this time."
Gholamhossein Nozari, Iran's oil minister, said: "Balance should be established between oil demand and supply. In addition to stabilising the oil price, we intend to increase its price."
Economists say that Iran, the second largest Opec producer after Saudi Arabia, has become increasingly dependent on high oil prices, some saying it now needs $70 to $75 a barrel for its crude to balance its books.
Kuwait, another Opec member, has warned that it will have to cut spending in its next budget if the price of its crude fell below $60 per barrel.
"The estimated budget of 19 billion dinar [$70.71bn] will not be affected, but the new budget could be affected depending on an increase or decrease of oil prices," Mustapha al-Shamali, Kuwait's finance minister, told al-Rai newspaper.
State news agency KUNA said Kuwait's crude oil fell to $59.15 on Thursday.
Nigeria has also been hit by the dramatic drop in world oil prices, prompting a revision in next year's budget, which is due to be debated in parliament next week.