By Jamie Robertson Business presenter, BBC World

If anyone imagined that investing in oil at a time of $70-plus-a-barrel oil prices was a guaranteed investment, BP's experience over the last few weeks has provided a salutary lesson.

Oil leaks, rusting pipes, and now an investigation by regulators into the allegations that it might have manipulated oil and gasoline prices have sent its shares down 8.6% this month - back to where they were at the beginning of the year.

The rest of the oil sector is not immune to such bad press. Exxon is down 3.6% this month.

Out of the BBC's Global 30 index only China's CNOOC showed a gain, just 0.1%, and that was after record first-half profits and much excitement over the opening of its two new oilfields in the second half of the year.

Strikes and shortages

BHP Billiton has also been having production problems at the Escondida copper mine in Chile, where workers are demanding pay rises in line with copper prices.

BP is now replacing 16 miles of pipeline at the Prudhoe Bay site

The Anglo-Australian firm is in the painful position of watching copper prices break new records because of the strike and supply shortages, just as its sales fall away and its shares slip 2.3%.

The problems at BP (whose weighting accounts for some 6% of the Global 30 Index) served to pull the whole European sector down, making it look a lot worse than it was compared to the US and Asia.

For once risers and fallers were equally distributed about the globe.

However among those losers BP was well out in front of the pack, with the Hong Kong trading group Hutchison Whampoa the second-biggest faller, down just 3.3% after it admitted it was going to take another year before it could bring its third generation mobile phone business to break-even point.

BIGGEST GAINERS IN AUGUST Proctor & Gamble: 8.81% Electricite de France: 7.68% Nokia: 6.18% Tesco: 5.47% Anglo American: 5.38%

The 3G unit is the tail that has been wagging the dog of Hutchison's massive trading conglomerate over the last two years.

While it promises immense profits one sunny day, until then earnings will rise purely though asset sales. First half profits doubled thanks to the sale of a fifth of its port unit, the world's biggest, to Singapore's PSA International.

Tokyo trading

The retail industry has been having a busy month, although it's done precious little good for the share prices.

Japan's Seven & I Holdings, which owns the 7-Eleven convenience store chain, bought out White Hen Pantry for $35 million to strengthen its U.S. operations.

Japanese retailers are chasing more mergers and acquisitions as the intense competition at home (and a falling population) caps their domestic growth.

Before this acquisition Seven & I bought out 7-Eleven of the United States last year, and later, among others, department store Millennium Retailing. Seven & I is down 3.6% this month.

Meanwhile Wal-Mart has said it may join the chase to buy part of Daiei, which is also being pursued by Aeon. Daiei was once Japan's largest retailer but has long been ground down by a trillion yen's worth of debt.

Proctor & Gamble is gaining from its merger with razor-maker Gillette

The market is not that impressed by Wal-Mart's ambitions and has marked its shares down 0.8% this month.

The giant US retail group has been in Japan since 2002 but has yet to turn a profit, while it has been pulling out of other overseas markets, most notably South Korea and Germany.

Razor-sharp performance

Having ignored the stock for about a year investors have started to buy into Proctor & Gamble with a vengeance sending its shares up 8.1% this month.

The reason was the fourth quarter results which seemed to show that the $60bn Gillette merger last year is working and will start to produce even better savings and profits next year.

Even without the merger P&G's sales are up 8% and it is confidently rolling out new toothpastes, razors and household cleaners.

BIGGEST LOSERS IN AUGUST BP -8.60% Seven & I Holdings -3.60% Exxon Mobil -3.56% Hutchison Whampoa -3.25% BHP Billiton -2.29%

Just behind P&G is Electricite de France (EdF) which rose 7.7% on the news at the start of the month that it's being allowed a 1.7% increase for regulated power prices in France, where the company has four times the sales it has in Britain, its next-largest market.

In July it said would raise UK household prices by 8%.

On a less welcome note for EdF, a fierce debate is boiling in France over whether some companies that buy electricity on the unregulated market should revert to regulated prices because they are struggling to cope with rising power costs.

The measure will be discussed in France's parliament as part of an energy bill required to allow state-controlled Gaz de France to merge with Suez.

Zune progress

There also seems to be a ring of confidence around Microsoft's share price, which gained 5.3% this month.

The news is not all good - Google announced new software products this month in direct competition to Microsoft - but there are glimpses of progress.

There's increasing publicity over its Zune music player, with Toshiba agreeing to manufacture it and record label EMI signing a deal to preload music videos on to it.

Meanwhile, Amazon has started to taking orders for the software giant's much-delayed Vista operating system.

Despite the gloomy set of car sales figures from the US this month Toyota (up 1.2%) as usual came out smiling with news that as overall sales collapsed by 17% in June, its sales rose 10%.

While the market for Toyota in India is a minnow in comparison, its performance there is not so rosy - sales are actually falling, although it still says it wants to gain a 15% share of the market in ten years.