Ford Motor Co. and PSA Peugeot Citroen today announced an extension to their decade-long relationship that has resulted in the production of over 6.5 million diesel engines for the European market.

The sixth phase of the partnership, dubbed the “Gemini” co-operation, involves the development and production of a range of Euro 6-compliant diesel engines for consumer and commercial use.

The new lineup of diesel engines, slated to go into production in 2013, will deliver improved fuel economy, reduced carbon-dioxide emissions and enhanced performance attributes, the auto makers say.

Overall investment for the project is expected to total £300 million ($408 million).

“By working closely together over the past decade, we have achieved our objective, and the co-operation has proved to be one of the most enduring and successful partnerships in the global automotive industry,” Ford of Europe CEO Stephen Odell, says in a statement. “Together we are the largest manufacturer of high-technology diesel engines in the world.”