The world is experiencing a reverse oil shock. Crude prices, which were more than US$100 a barrel as recently as July, have plunged by a third to under US$70.

The months-long price slide, from a sluggish global economy and a boom in US shale oil production, accelerated in the last few days after oil cartel Opec announced on November 27 that it would keep pumping rather than cut output - in a risky game of chicken with US producers to see who will blink first.

Obviously plunging oil prices is a bonus for consumers and companies when prices fall at the pump, giving individuals more spending money and lowering costs for many businesses, particularly airlines.

Christine Lagarde, head of the International Monetary Fund Managing Director, said on December 2 that "There will be winners and losers, but on a net basis it's good news for the global economy."

Here's a closer look at who wins and who loses:

RICH OIL EXPORTERS

Saudi Arabia, Opec's biggest producer, and Qatar and Kuwait, who have the lowest production costs, are potential winners in the battle with their US rivals. These three will definitely benefit if Opec can wrestle back market share from US producers longer-term.

The problem for them is that Opec's once mighty influence on the oil market has declined and the forces of demand and supply now rule. Bloomberg estimates that global oil production is running at just under 31 million barrels, while global demand is running at just over 29 million barrels a day.

Opec's gamble, therefore, may not succeed.

Verdict: Still out

POOR OIL EXPORTERS

The big losers when oil prices crash are Opec's poorer members that depend on oil exports for the bulk of their revenue.

Countries like Venezuela and Nigeria do not have the same low cost of production or sizable foreign reserves as Saudi Arabia does, and will be very hard pressed to maintain their social programmes. Once those social programmes are cut, there could be social strife that destabilises governments and the region.

In Venezuela, which argued vehemently for an Opec supply cut, oil production has been steadily declining for years so the combination of lower output and lower prices is already squeezing finances with the result that President Nicolas Maduro announced on Friday steep cuts to government spending - starting with his own salary.

In Nigeria, the naira tumbed to a fresh record low on Monday on fears over the impact of plunging oil prices on Africa's biggest economy.

The central bank devalued the currency by 8 per cent against the US dollar last Tuesday in a bid to halt a decline in the foreign reserves of Africa's leading energy producer, but has struggled to keep the currency in its target range since then, Reuters reported. The country's woes are excacerbated by the fact that Nigeria's oil savings actually fell when oil prices were at record highs, partly owing to theft of its oil by criminal gangs, hurting output.

Verdict: Lose

RUSSIA

The economy was already sliding into recession under the impact of Western sanctions. Oil and gas provide 68 per cent of Russia's exports and 50 per cent of its federal budget, so the country will be hit hard.

For Russian consumers, pump prices have actually gone up because the falling ruble has increased inflation. In local money, 95-octane gasoline costs now costs 35.99 rubles a litre in Moscow, up from 35.53 per litre two months ago, AP reported.

Declining energy prices had already sharply depressed the ruble. Following Thursday's OPEC decision meeting, it dropped another 3.6 per cent for a 35 per cent loss against the U.S. dollar so far this year.

Verdict: Lose

THE UNITED STATES

As the world's largest oil consumer, it stands to benefit the most.

Drivers in the US are enjoying the lowest gasoline prices since 2010 with pump prices as low as US$2.79 on Friday. Tom Kloza, chief oil analyst at the Oil Price Information Service, told news agency AP he expects gas to eventually be a full US$1 per gallon below its June peak of about US$3.70 a gallon. That would save the average American household about US$60 a month for those that burn 60 gallons of fuel.

But for US oil companies behind a production boom, the news is not so good. Crude produced in Canadian oil sands, deep offshore in the Gulf of Mexico and in some U.S. onshore shale formations is some of the most expensive oil to produce in the world, said AP. Drillers will have to cut back - some may even go under - if profit margins are squeezed hard enough. Shares of Continental Resources Co., one of the biggest US producers, fell 20 per cent on Friday, a day that virtually every energy company's stock fell.

It's not just energy stocks feeling the heat. US funds have played a big part in bankrolling the US shale boom, gobbling up billions of dollars of junk-rated bonds issued by energy companies to rapidly expand production, Reuters reported. In recent weeks, prices of some of these bonds have collapsed as oil prices have tumbled by a third since June to four-year lows, raising fears of a new, albeit smaller, credit crisis.

Verdict: Overall win

EUROPE

Sluggish Euro zone economies will get a small boost from lower oil prices boosting consumer and business spending.

In Germany, the price of Super E10 fuel has fallen from 1.53 euros per litre at the start of September to 1.42 euros per litre this week, AP reported.

On the other hand, the oil price slide is depressing consumer prices that are already close to stagnating. "Lowflation" or weak inflation is a real threat to the euro zone especially for economies like Greece still struggling to reduce debt. It is also a problem for the European Central Bank, which wants to boost inflation from just 0.3 per cent currently to around 2 per cent.

The few European oil producing countries - mainly Britain and Norway in the North Sea - face a drop in revenues that could balance out the positives of cheaper fuel, AP noted.

Verdict: Double-edged sword

JAPAN

Japan is another big net importer of oil but cheaper crude prices have been slow to filter down to consumers, AP reported. The recent decline in the yen has also offset the savings from lower oil prices.

Regular gasoline which cost US$1.40 a litre at the Esso station in Shimbashi, near Tokyo's Ginza shopping strip, actually cost slightly more - US$1.44 a litre - on Friday.

Pump prices should eventually come down but this will make it harder for the government to fight falling consumer prices or deflation.

Verdict: Overall draw

CHINA

Chinese consumers and businesses are benefiting from cheaper fuel. The government has cut pump prices repeatedly this year and on Friday, highest grade gasoline cost US$1.20 a litre in the capital, down from US$1.35 a litre in June, AP reported.

The price slide has also given China, the second-largest oil consumer, the opportunity to build up its strategic oil reserves at lower costs. It is also offering Chinese energy companies the chance to buy distressed energy assets.

Verdict: Win

OTHER ASIAN ECONOMIES

Elsewhere in Asia, the impact is varied.

In big oil importers like Singapore, slumping crude prices will lower inflationary pressures and benefit households and most businesses. But a prolonged decline will hurt key sectors of the economy like marine and offshore engineering and petroleum refining.

In Indonesia, fuel costs have risen because the government has cut subsidies, more than offsetting the decline in global oil prices. The higher prices triggered street protests, so the latest fall in crude prices may help ease tensions, according to AP.

Malaysia is among the few oil-exporting nations in Asia, so the drop is hurting its coffers but it has also helped the government to cut expensive fuel subsidies.

Verdict: Overall win