The attack on the heartland of Saudi Arabia's oil industry and damage to the world's biggest petroleum-processing facility has brought oil prices to their highest levels in almost four months.

Here are some information about the blow on oil supply and spare.

Why is it so troublesome for global oil supplies?

The strike on Saudi oil facilities on Saturday not only banged out more than half of the country's production, but also disconnected almost all the extra capacity readily available to restore for any major trouble in oil supplies worldwide.

The attack slashed 5.7 million barrels per day (bpd) of Saudi crude production, above 5 percent of the world's supply. However the attack also inhibited Saudi Arabia's capability to utilize the over 2 million bpd of spare oil production capacity it kept for emergencies.

The kingdom has quite a long time been the only foremost oil producing country that has kept important spare capacity that it could start up rapidly to recompense for any shortage in supply reasoned by war or natural calamity.

A lot of countries cannot pay to drill costly wells and establish infrastructure, then it become inactive.

Prior to the attack, the Organization of the Petroleum Exporting Countries (Opec) global supply cushion was just over 3.21 million barrels per day (bpd), as per the International Energy Agency (IEA).

Saudi Arabia - the defacto leader of Opec - had 2.27 million bpd of that capacity which leaves approximately 940,000 bpd of spare capacity, mostly held by Kuwait and the United Arab Emirates. Iraq and Angola also have some spare capacity. They may at the present bring that production online to assist plug some of the gap left by Saudi Arabia - but it won't be sufficient.

Haven't Opec and its allies been reducing production? Can't they simply revise those reductions?

Yes, Opec and its allies for example Russia have slash production to avoid prices from declining because the market has been oversupplied.

Those slashes intended to reduce supply  by 1.2 million bpd. But a great deal of that was from Saudi Arabia so it currently cannot be reversed fast.

Non-Opec members like Russia are pumping near ability, with possibly only 100,000-150,000 bpd of accessible extra production.

What about Iran?

Iran grasps spare capacity but it cannot obtain the oil to market because of sanctions forced by the government of US President Donald Trump.

Iran's exports have dropped over 2 million bpd since April.

According to Washington, Iran was behind Saturday's attack, so is doubtful to ease sanctions to let Iran to plug a gap it believes was formed by Tehran.

And Venezuela?

US sanctions have also affected the Venezuelan oil industry. But Venezuelan production has been in free-fall for years and state oil company PDVSA is improbable to be able to increase production greatly even if sanctions were reduced.

What on US shale? Can shale producers pump further?

The United States has become the world's top crude producer after years of quick development in supply from the shale sector, much of it pumped from fields in Texas. The US has also developed as an exporter, and shipped more crude to international markets in June than Saudi Arabia.

Shale producers can shift quickly to pump further when prices go up, and can fetch production online in a matter of months. That is a much faster time line than most usual oil production. If the Saudi outage looks like it will be long-lasting and oil prices rally considerably, then shale producers will lift output.

But even if shale producers pump extra, there are restrictions on how much the United States can export as oil ports are already close to capacity.

So what comes about now? What about oil in storage?

It all depends on how long the outage lasts.

Saudi Arabia, the United States and China all have hundreds of millions of barrels of oil in strategic storage. That is the storage that governments keep for exactly this scenario - to balance for unanticipated outages in supply.

They can discharge oil from strategic storage to meet demand and temper the blow on prices. US President Donald Trump said on Sunday he had authorised a discharge from the US Strategic Petroleum Reserve.

The IEA, which organizes energy policies of industrialised nations recommends all its members to keep the alike of 90 days of net oil imports in storage.

What occurs if there is one more supply disturbance?

Without spare capacity, future disturbances would origin oil prices to go up. A higher price over time will support producers to invest and pump more, while at the same time sinking consumption.

OPEC member Libya is in the centre of a civil war, which frightens its ability to continue pumping oil. Another big Libyan disturbance would add to the shocks and highlight the shortage of spare capacity.
Nigerian exports have also suffered from disturbances.

Attack puts limelight on global disaster stockpiles 

The United States is the world's key oil consumer and a top producer. The US SPR, held in underground storage caverns on the Texas and Louisiana coasts, now contains nearly 645 million barrels, or about the amount the United States uses in a month.

The United States has more 416.1 million barrels sitting in commercial storage, according to the US Energy Information Administration's latest data. Those are held by oil producers, refiners and traders.

Saudi Arabia has declared that it would use oil in storage to load tankers for customers. The Country has about 188 million barrels in reserve, according to Rapidan Energy Group.

The International Energy Agency, that manages the energy policies of industrialized nations, toldon Saturday that it was in contact with main producing and consuming countries but that oil markets were well supplied..

Robert Ryan, chief commodity and energy strategist at Montreal-based BCA Research, calculated China's SPR at 510  million barrels while Seng Yick Tee, an analyst at SIA Energy estimated that China at present holds 325 million barrels of  SPR.

According to Ryan, it was a matter of time before governments would run through their commercial supplies and be needed to tap emergency reserves.

"The market could tighten significantly if the outage if the outage is indeed weeks and not days. You will see SPR draws. Arguably the world is dependent on strategic reserves right now," he said.