While it is now the second-biggest manufacturing group in Europe, the value of the PSA Group as a brand is still outside the top 10 car manufacturers in the world, according to a specialist valuation and strategy consultant.
Robert Haigh, of Brand Finance, said: "We would expect the total value of the portfolio post-merger to be well in excess of 10 billion dollars (£8.1 billion).
"Given the cost savings and likely growth, this could easily be as high as $12bn.
"General Motors (GM) will see the value of its brand portfolio suffer a similar decline that will see it drop below Nissan and Ford.
"This doesn't mean it is necessarily a bad idea for GM, however.
"They have clearly been unable to exploit the brand equity of Vauxhall and Opel as effectively as they would have liked, so freeing up cash to invest in other brands may be wise and will enable brand value growth in other areas of the business."
The firm, which takes into account factors such as investment in marketing, staff satisfaction and environmental performance as well as sales figures, ranked PSA 13th in the world, behind Volkswagen.
Mr Haigh said value depends on both revenue and brand strength.
He added: "Manufacturers of more expensive vehicles, such as Daimler and BMW, clearly have a higher revenue per car and so a higher brand value per car."