Automakers' alliances don't always work, even when the synergy looks right, according to General Motors president and CEO Rick Wagoner.

"We have had some good examples of co-operation and some that haven't worked out, " he said at the London motor show.

"Hopefully, that experience will enable us to make sure that as we look, going forward, at potential joint projects or equity co-operations that we will be able to learn from the past what kind of things work best for us and what don't and I think that's probably true for every manufacturer."

He added that continuing consolidation in the industry was likely.

"When and who is the tougher question, and will it be done without occasional problems through the process and history would suggest no.

"It is not as smooth a road as you might expect but, from GM's side, we have had so much experience now, both positive and ones that haven't worked out that well, I think we've got a pretty good sense of the kind of things and the kind of circumstances where we can get the right kind of value for our shareholders."

He said the relationship with Fiat generated "huge synergies" - the purchasing and power train joint ventures - on a 50/50 equity basis.

"It generated huge value for us and, I believe, for Fiat, " Wagoner said. "What didn't work so well was the equity ownership and then there were successive changes in the management of Fiat - they had a different vision for their company and so it came apart on that point.

"I would say if you looked at the 50/50 work on the powertrain and purchasing joint ventures, during the period they were operating they actually generated pretty good value.

"One size doesn't fit all here, you have to look at the circumstances. You've got to make sure the stuff you're working on really has true potential to create value, and schedules, and who's going to give up doing what. These are important aspects."

Graeme Roberts