[ptaipale]

Huge amount of different tests. Manual gearboxes are generally more efficient, but not in all situations, and the modern dual-clutch automatic boxes outperform manual transmission in many cases.

But overall, there are hydraulic losses in classic planetary automatic gearboxes, and they are also heavier.

For instance,

http://www.consumerreports.org/cro/2012/01/save-gas-and-mone...

Personal experience: I regretted buying a Renault Laguna with automatic box. Horrible fuel economy. Even the torque lock didn't help, also highway economy was quite bad which was very surprising. Other than that, a nice car.