Here's what OPEC ministers are saying at the oil cartel's landmark meeting

Oil-producing nations appeared to be on the brink of securing a landmark output agreement in Vienna on Thursday, amid calls from the U.S., China and India to cool down prices and support the global economy by producing more crude.

Energy ministers are gathering in Austria this week to determine the future of OPEC's 18-month-old agreement with Russia and other producers to limit oil output. The strategy has cleared a global supply overhang, but with oil prices recently soaring to multi-year highs, energy ministers are trying to reach a consensus on easing the output cap to prevent the market from overheating.

Ahead of Friday's pivotal meeting, CNBC takes a look at the mood among some of the leading voices in the Austrian capital.

Saudi Arabia's Energy Minister Khalid Al-Falih told CNBC on Thursday that he was "optimistic" OPEC could reach a consensus on production policy this week, adding that there was a "spirit of co-operation" among the Middle East-dominated group.

He also said consumers would soon demand more oil in the second half of 2018, so OPEC would need to discuss how to raise production by around 1 million barrels per day (bpd) in order to bring compliance back to normal levels.

When asked whether Iran —which has so far been the main opponent to a new deal — was now on board ahead of the summit, Al-Falih replied: "We will find out."

De-facto OPEC leader and top crude exporter, Saudi Arabia, has been pushing, alongside Russia, for the cartel to loosen its supply controls — which were introduced in January 2017 in order to prop up prices.

However, other OPEC members, including Iran, Iraq and Venezuela, are thought to be reluctant to change from the current parameters of the deal.

The meeting comes at a time of heightened pressure from President Donald Trump, who has publicly complained that OPEC is to blame for crude prices recently soaring to multi-year highs. OPEC members have said that the group is not a political organization, however.

The United Arab Emirates' minister of energy and industry, and OPEC president, Suhail Al- Mazrouei reiterated that view, telling CNBC Thursday: "This is not a political organization, this is a commercial organization and as I told you earlier we are not going to politicize the organization.

"We will make good progress like we do always and everyone is happy that we're together with non-OPEC," he added.

OPEC reached a historic agreement with Russia and other non-members in late 2016 to keep 1.8 million barrels per day off the market. That arrangement has cleared a global glut of crude oil that sent oil prices tumbling from more than $100 a barrel in 2014 to less than $30 a barrel in 2016.

International benchmark Brent crude has since rebounded to about $75 a barrel.

"I am confident that we will reach some sort of agreement," Iraq's Oil Minister Jabbar Ali al-Luaibi told CNBC Thursday.

Alongside Venezuela, Iraq is thought to be opposed to a relaxation of supply cuts, fearing that higher oil production will lead to a slump in crude prices.

On Tuesday, Iranian Oil Minister Bijan Zanganeh said he doubted OPEC could reach a deal this week. He also railed against Saudi ally President Donald Trump, saying American sanctions on OPEC members Iran and Venezuela had sent oil prices higher.

But on Wednesday evening, Zanganeh told CNBC that he was feeling "very good" about OPEC's production levels.

Zanganeh is reportedly due to hold separate talks with Russian Energy Minister Alexander Novak Thursday.

"It's really important they get the message right because let's remember what has been happening over the course of last two years as they put this policy in place. They've built up a whole lot of credibility as an organization that could actually move the market so they don't want to lose that," Michael Cohen, director of energy market research at Barclays, told CNBC on Thursday.