By Jamie Robertson Business presenter, BBC World

Just when the markets seemed to have got over their fears of high interest rates the spectre of spiralling energy costs has returned to give the world's biggest companies a case of serious jitters.

During the course of July the BBC's Global 30 rose a modest 0.74%.

The reasons for the energy problem have been raked over by every analyst from New York to New Zealand - the Middle East crisis, surging growth in China and India and soaring temperatures in the Northern hemisphere.

So, put your money into energy companies?

The Global 30 thought otherwise.

Electricity de France shares fell 3.2% and Tokyo Electric was down 3.6%.

Exelon in the US alone made a gain, just 0.9%.

In fact Japanese investors are not so much by the energy crisis but by the novel spectacle of rising interest rates: rates there rose last month for the first time in six years.

Biggest gainers in July China Mobile (Red Chip) 11.61% Exxon Mobil Corporation 9.38% Tesco 7.63% AT&T 6.52% CNOOC (Red Chip) 5.56%

It was a mere 0.25%, but Tsunehisa Katsumata, Tokyo Electric's president said a 1% rise in short term rates would add about $50m to costs.

As for EdF it has been struggling in the heat: its supplies to central London collapsed under the strain of massive air conditioner use at the end of July, its French power plants have been restricted in the amount of water they can use for coolant and it has been forced to buy peak-hour electricity from Italy.

Costs for many of the energy companies are rising fast, especially if they, like EdF, have to buy in extra supply, according to Mark Watton, European Energy analysts at BNP Paribas.

"Most of the companies across Europe sell their energy way in advance and they don't sell into the day-to-day spot prices - so they can't instantly put up prices to their customers," he says.

"If the prices stay high for a long time, then they will be able to put up their prices and play catch-up."

Companies such as the chemicals group Du Pont in the US also found the going tough.

As crude and its multitude of derivatives shot up in price, margins were squeezed right across its chemicals businesses.

As a result of this and a stalling market for its agricultural products, Du Pont, instead of raising its forecasts for this year's profits, said it would be much the same as it was predicting three months ago.

Mobile spread

Of course the natural beneficiaries of a rising oil price had a good month: Exxon rose 9.4%, BP 1.4% and CNOOC of China 5.6%, with Exxon's second best quarterly results yet giving its shares an added impetus.

Biggest losers in July Vodafone Group -11.74% Wal-Mart Stores -8.49% Siemens AG -8.28% Du Pont De Nemours -5.56% Nokia -3.80%

But the best performer on the Global 30 was China Mobile, which is on a relentless bull run ahead of the granting of licences for China's third generation mobile phone networks later this year.

However, there has been some speculation they may be delayed until 2007 as the regulators ponder whether to use home-grown or foreign technology.

Whatever the outcome, China Mobile and its rival China Unicom will get those licences and first mover advantage in the biggest mobile market on earth.

As an illustration of this - for the third month in a row China Mobile added a record number of conventional mobile subscribers - 4.4 million.

Global expansion

More satisfaction for Tesco shareholders in the UK as its shares rose 9% on the month, and it increased its domestic market share to a record 31.5%.

But in truth, investors are more interested in its future overseas, and July saw a flurry of news stories on its offshore ambitions: it said it had completed a deal to buy Casino's 279 Polish "Leader Price" stores, was actively planning to open more stores in Turkey and China next year, conducting feasibility studies on the Indian market, and opening a chain of convenience stores in California in 2007.

Even though the Dow Jones and the Nasdaq have failed to shine over the last month, the American stocks on the global 30 have had their best run for months, rising on average by 2%.

Aside from Exxon, the big gainers were AT&T (up 6.9%), Johnson & Johnson (up 4.1%) and Microsoft (up 3.2%).

AT&T 's rise is thanks to an 81% rise in second quarter profits and a plan to buy back $10bn worth of shares.

AT&T only arrived in the Global 30 last month thanks to the $16.5bn merger with SBC last November, and much of the optimism is coming from Cingular Wireless, the country's largest mobile phone services company and which it will gain complete control of by buying its owner BellSouth for $67bn.

Losers

In sharp contrast, Verizon announced on the last day of the month that it will not be buying complete control of its Verizon Wireless joint venture from Vodafone.

Verizon dropped out of the Global 30 last month - to be replaced by AT&T.

Vodafone shares are the worst performer on the Index, down 11.7%.

Johnson & Johnson's results were also good, with profits up 9% in the second quarter as it sold more medical devices, but fewer drugs; and Microsoft had a good month as it forecast that the Personal Computer was doomed but that the company's future lay elsewhere, on the internet, in digital downloading kits like its Zune music player and its Xbox game.

Not all US stocks did well - most notable among them was WalMart (down 8.5%) which pulled out of Germany last week, selling its stores to its rival Metro.

It was also forced to accept unions at its Chinese stores, its UK subsidiary Asda has been losing market share to Tesco and Sainsbury's and it has agreed to sell off its South Korean operation.

On top of that Chicago's City council voted to force big retail stores to pay their workers almost double the minimum wage

Also on the losers' list was Siemens, the German engineering group, which has been restructuring, planning job cuts and selling off units such as its mobile phone business.