Toyota is planning to supply BMW with hybrid drive-train systems and hydrogen fuel-cell technology, according to reports in Japan.
It signifies a strengthening of a green car development deal forged last December.
On the face of it, the deal would make sense as it would give Toyota economies of scale for its petrol-electric hybrid systems, according to reports in 'Automotive News Europe'.
Details of the deal were reported last week by Japan's Nikkei business daily and repeated over the weekend by Germany's 'Der Spiegel' magazine.
The two companies are to make an announcement this week.