The oil price has leapt 23% in the past six months. Global demand has been strong and investors are growing increasingly worried about Iran’s nuclear programme, because it has the world’s third-largest oil reserves.

Richard Berner of Morgan Stanley, the American investment bank, said: “A synchronised rebound in China, the US and Europe has followed the growth pause at the end of last year and boosted demand.

Supply remains tight and Saudi Arabia’s spare production capacity is partially an illusion — it is mostly in heavy crude, for which there is less demand.

“But the recent rise in the oil price cannot be fully explained by supply-and-demand conditions. Political uncertainties, of which Iranian nuclear ambitions are the most important, have increased.”

Berner thinks oil could peak at $80 in September and even hit $100 in the worst-case scenario: an open confrontation between Iran and the rest of the world, leading to an economic or military blockade.

However, Jim Wood Smith, head of research at Christows, a stockbroker, said: “It is likely that the Iranian situation will drive the price higher, but it could be the final spike.

“Much of the production capacity that was disrupted by Hurricane Katrina last year is due to come back on stream in the autumn, while the oil companies have massively raised investment levels. The longer-term prognosis is therefore that the oil price should weaken, but it is odds on to hit $80 first.”

The obvious way to profit from an oil-price spike is to buy shares in oil companies such as BP, Shell or the Irish oil company Tullow. Joe Gill, head of equity research at Goodbody, said: “The best way to look at the way oil prices have affected the Irish market is to look at Tullow, up 60% in the year to date, and Ryanair, down 19%.”

Oil prices are notoriously difficult to call. Airline analysts, for example, had just got used to the idea of kerosene staying over $700 when it dropped to $691. High oil prices have been poor for the Irish stock market, with its heavy reliance on financial stocks, but it has buoyed European and world indices with a higher component of commodity stocks.

According to Gill, if the price is driven higher by supply issues, there is less cause for concern, as this is itself a signal of strong demand within the global economy.

For example, energy costs are a big concern for a company such as cement producer CRH. But the company has been able to pass on higher prices to customers, a reflection of the general economic buoyancy.

While the oil sector has performed well in the past six months with a gain of 17%, it has lagged behind the mining sector, which is up 51% on the back of rising metals prices.

Tony Shepherd of Charles Stanley, a stockbroker, said: “Although crude has been bubbling higher, share prices in the oil sector are based on a long-term oil price of only $45, so there could be some catching up to do.”

Alternatively, you could invest in smaller oil-services companies that supply the oil giants with facilities such as engineering, construction and research. They are in high demand because the likes of BP and Shell are increasing their spending on exploring and developing new sources of oil.

Patrick Evershed, the manager of the New Star Select Opportunities fund, suggests Wood Group and Petrofac, which supply engineering services, and Sondex, a drilling company.

“If the price of oil goes up, these companies ought to perform well,” he said, “and if the price falls they will still be in a good position because the major oil companies are committed to the extra spending.”

Companies producing renewable energy, such as wind, wave and solar power, should also be big winners if the oil price stays high, because companies will seek cheaper sources of energy.

NTR is the leading Irish company in this area, but the shares are not traded on an exchange and, as a result, are difficult to acquire.

Most of the big alternative- energy companies are North American, but Clipper Windpower, a Californian turbine company, has a listing on London’s Alternative Investment Market (AIM). Another option is the Merrill Lynch New Energy Technology fund, which has gained 56% in the past year and 239% in the past three years.

Another proxy for the alternative energy sector is to track the commodities used to produce ethanol such as corn, sugar and wheat.

Stanhope Capital, an investment adviser, said: “High oil prices are here to stay and this will create growing opportunities in alternative energies. Investors should consider commodities, including biofuels, because they do not tend to move in line with other assets.”

Analysts said the high oil price could lead to a revival of the coal industry. Bradley Mitchell of Royal London Asset Management said: “By 2010, China will be a net importer of coal, suggesting we could be in for a period of rising prices. Watch out for open-cast mines receiving planning permission.”

The main beneficiaries would be mining groups with coal divisions such as BHP Billiton, Anglo American and Rio Tinto, all listed in London.

Nuclear power could also make a comeback and has even got back onto the political agenda in Ireland. Nuclear already provides 20% of Britain’s electricity, and the Labour party there has indicated it would be prepared to build more plants. This would benefit British Energy.

If the oil price stays high the big losers will be those that use a large amount of fuel, such as transport companies and food producers.

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