The automobile industry is especially prone to corruption because of business practices that encourage suppliers to put up big money to win contracts from carmakers, a German researcher claims.

Immense pressure on sup-pliers to cut costs or face losing contracts also compounds the potential for bribery and other illicit payments, said Wolfgang Meinig, head of the Automotive Industry Research Centre in Bamberg.

"For more than ten years it has been common practice in contract negotiations for carmakers to demand entirely officially sums worth millions from suppliers just so they can make the short list for a contract or a follow-on contract," he said.

"In my view that is fertile ground for corruption," he said. "A purchasing official then asks himself: If my company can rake in millions so easily, why can't I?"

His comments follow a widening investigation by German prosecutors into whether suppliers bribed purchasing managers for years to win contracts.

French carmaker Faurecia is at the centre of the probe, which also involves staff or former employees at Volkswagen, Audi and BMW, prosecutors have said.

Six suppliers including Faurecia are under investigation by Munich prosecutors, prosecutor Anton Winkler confirmed earlier this week.

Germany's VDA auto industry association has said other sectors are just as likely to see bribery attempts, according to public statistics. "The decisive thing is taking determined action against it," a VDA spokesman said on Monday.

But Wolfgang Meinig disagreed.

"I think corruption is a particularly grave problem in the auto industry, even if some people in the sector don't want to hear this," he said. "The dependence between manufacturers and suppliers is so strong in hardly any other business."

He cited in particular "quick savings" worth millions that suppliers are asked to put up to take part in contract tenders.