Liam Dann: Oil price slump points to relief at the pump in New Zealand

A pump operates in a Texas oil field. Photo / AP

Global oil prices have slumped nearly 20 per cent in the past six weeks pointing to lower pump prices for kiwis in the days ahead.

But while that's good news for consumers the downside is that it reflects growing worries about strength of the global economy.

Brent crude oil dipped below US$60 a barrel this week - off 18 per cent since late April.

The other key benchmark, West Texas Crude oil is off 22 per cent in the same period.

Prices for both commodities spiked briefly overnight, after attacks on oil tankers off the Gulf of Oman spooked markets.

Both have already started falling again, although the attacks do highlight just how volatile oil markets can be.

Longer term, the fall has big implications, not just for drivers' wallets, but for inflation and the interest rate outlook.

Oil prices had been rising sharply for through the first four months of this year on geo-political tensions.

The new US sanctions against Iran and the disruptive impact of a civil war in Libya had weighed on global supply expectations.

But growing concern about the trade war and slowing global demand has combined with increasing US production to put prices sharply into reverse.

It is becoming a familiar pattern.

Last year oil prices surged through to October and threatening to push local pump prices as high as $3 a litre - then the market slumped (along with share markets) .

From more than US$80 a barrel at peak in October, the price dropped by a third and we ended the year paying closer to $2 a litre at pump.

A litre of 91 octane is currently about $2.20 according to the AA's Petrol Watch.

Oil started rising again in January. But the rally was even shorter lived than last year.

A sharp drop in demand seems to be the biggest concern this year.

Investment banks have slashed their consumption forecasts.

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Morgan Stanley said this week it expects growth of one million barrels a day, while JPMorgan sees 800,000 barrels a day.

That would be the lowest growth rate since 2011, Bloomberg reports.

Meanwhile, efforts by OPEC nation's to limit supply have been hampered by rising US shale oil production - which has been coming back online since the big slump of 2014.

The historic slump in fuel prices, which began in 2014, saw prices fall more than 40 per cent.

It exacerbated deflationary conditions around the world, prolonging a period of historically low interest rates.

While this is often viewed as good news for consumers it reflects a world that now struggles to generate strong economic growth for prolonged periods.

The rallies and slumps on oil markets in the past few years bear a similarity to the attempts by central banks to lift interest rates back to more normal levels.

Every time the global economy looks to be starting to boom, and central banks look to lift rates, sentiment shifts reversing the trend.

In the past few months the US Federal Reserve has put interest rate hikes on hold and now looks more likely to cut them this year.

Both the Australian and New Zealand Reserve Bank's have cut rates.

As lower fuel prices flow through to inflation data it wil make it even easier for the central banks to maintain low rates.

Petrol prices are due to fall as global oil markets slump. Photo / File

That adds up to more stimulus for the economy - albeit against a backdrop of low business confidence globally and locally.

Whether the slump continues depend on geo-political factors and further tanker attacks could see it rising again.

But it's all still a world away from a decade ago it was normal to see analysts predicting oil would hit US$150.

It has become increasingly obvious that the complexities of oil markets and petrol prices have little to do with the black stuff actually running out - a prospect that dominated thinking in the 1970s and 1980s.

Sadly for those concerned about fossil fuel consumption and global warming the economics of oil production have improved exponentially to meet demand.

It look like our efforts to reduce reliance on oil will need to be self imposed.