Though most BMW and Toyota owners probably don’t realize it, the two automakers are already partners in developing next-generation lithium-ion battery technology. In exchange for access to Toyota's battery technology, BMW has agreed to supply Toyota with its advanced-technology, low-emission  1.6-liter and 2.0-liter diesel engines for use in European Toyota models.

Now comes word from Spiegel Online, seemingly confirmed by Japan's Nikkei daily newspaper, that the two automakers are about to get even closer. Details are still sketchy, but Spiegel speculates that an announcement is imminent and likely to center around Toyota’s hybrid and hydrogen fuel cell technology.

The timing for BMW couldn’t be better. The German automaker is about to lose hybrid development partner PSA Peugeot Citroen, as the French automaker is said to be strengthening ties to Opel, and hence General Motors. That leaves BMW in need of a hybrid partner, and Toyota is arguably the leader in this segment.

Such an agreement is win-win for both BMW and Toyota. BMW gets the benefit of Toyota’s mature hybrid technology, while Toyota gets to claim an upscale partner in BMW. Depending upon BMW’s component purchase volume, Toyota may even realize a cost saving by building hybrid components in higher volumes.

Look for a joint announcement from both Toyota’s president, Akio Toyoda, and BMW’s CEO, Norbert Reithofer, later this week.