This shows the perils of investing in even the best price-taking businesses (ones that have no power over their prices, and simply sell at the market price), as commodity revenues can be slashed on the back of a simple shift in the supply and demand dynamic.

So when the Organisation of Petroleum Exporting Countries (OPEC) decides it's time to start an oversupply-based price war with US shale oil producers, it's watch out below for oil investors.

The key question for medium-term focused investors is will prices recover to higher levels, or is energy now in a geopolitical bear market and where should investors look for better returns?

The new American century

The shale energy revolution powering the US to energy independence is no secret, but only now is its runaway success taking its toll on global oil prices.

Closer to the point is that fracking and an abundance of cheap energy have benefited the US on almost every level over the last few years. Companies, consumers, manufacturers and equity investors alike have been prime beneficiaries of the cheap energy tailwind through 2014 and before.

With US shale oil production unlikely to decrease and OPEC unlikely to back down from its adversarial strategy of refusing to cut supply, Australian oil investors are caught between a rock and hard place right now.

The irony is that the big winner from OPEC's intransigence may be the wider US economy and equity markets moving into 2015, with crude oil producing nations and investors helping to foot the bill. All this while the weaker oil-producing emerging-market nations OPEC largely represents feel the economic squeeze more than ever.

In response Australian equity investors should look towards stocks with a consumer focus and US exposure, a standout option being retail and real estate business Westfield Corporation (ASX:WFD). Another business to consider is the world's largest packaging business Amcor (ASX:AMC). Currently valued at more than $15 billion it has benefited from higher volumes in North America in 2014 and the strengthening US dollar.

Moreover, the packing giant has hit a growth sweet spot as falling oil prices mean reduced manufacturing and raw materials costs, while US economic growth means greater consumer demand for its food, beverage and household products. Notably, both Westfield and Amcor have returned around 25 per cent to investors since the end of June, a period which has seen the ASX track the oil price significantly lower.

Lower for longer

Investors can expect these kind of consumer-focused stocks to benefit so long as the oil price remains relatively low in the year ahead. While bargain hunters in the energy sector who effectively speculate on the future price of global commodities are playing a high-stakes game given OPEC's current position.

If you add in the unknown future potential of shale oil globally and the political will in the US to support energy independence, then the long-term outlook for conventional oil prices looks decidedly patchy.

Many investors may conclude that the outlook for ASX-listed energy businesses in 2015 is tough. The best alternatives may be in the healthcare and industrials space with plenty of leverage to a weaker Australian dollar.

Foolish takeaway

Falling oil prices also mean lower inflation given the commodity's key role in consumer price indices within Australia and the wider world. A low inflation environment has fuelled growing speculation that the Reserve Bank's next move may be to cut cash rates in an attempt to kick-start the domestic economy.

That means the income hunt may run stronger than ever in 2015, with high-yielding equities on sustainable earnings trajectories likely to be the prime beneficiaries.

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Tom Richardson is a Motley Fool writer/analyst. He has an interest in Westfield Corporation. You can follow The Motley Fool on Twitter @TheMotleyFoolAu. The Motley Fool's purpose is to educate, amuse and enrich investors. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.