Porsche on Tuesday said first-half profit leapt fourfold owing to its stake in Volkswagen, but that sales were down and that it could not give a full-year forecast.

Net profit jumped to to EUR5.5bn ($US7.3bn) in the six months from August to January, mainly as a result of a spike in the value of VW shares in October, the company told AFP.

Porsche owns 50% of VW, the biggest European car maker, and wants to raise that holding to 75%.

In its 2007/2008 fiscal year, Porsche had reported a first half profit of EUR1.26bn.

Pre-tax profit climbed to EUR7.34bn from EUR1.66bn meanwhile, a result that also stemmed largely from transactions in cash-settled options on VW shares.

Cash-settled options are stock option contracts under which settlement is done via the payment of cash equal to the difference between the market value and the contractual value when the option is exercised or expires, AFP noted.

Porsche has used such VW-based instruments to make huge profits in the past two years, and they contributed EUR6.84bn to the group’s first half results this time around.

But the company warned that because the sum earned depended on the price of VW shares, “the amount could decrease again and could, by the end of the business year, be less than the half-year amount.”

Other earnings from VW added EUR444.4m to Porsche’s bottom line, slightly less than during the same period a year earlier.

Sales of Porsche’s own cars fell meanwhile by 26.7% to 34,266 vehicles.

For the full year, Porsche said no reliable forecast was possible, with neither Porsche nor VW able to escape the effects of a sector-wide slump, although VW expected to do better than rivals.

The company has rolled over a EUR10bn credit line from a consortium of banks, and another EUR2.5bn could be added “to support the achievement of strategic goals and also to meet future capital requirements,” the automaker told AFP.