Without the hybrid option, the 2007 Aura with a 4-speed automatic, six-cylinder, 3.5L gets 20/30 mpg city/highway. The Auto( S6), 6 cylinder, 3.6 L gets 20/28. Sit down in the hybrid and these numbers jump to an estimated 28/35. Those five to eight mpg are what GM's mild hybrid adds, and, as a Kicking Tires reader added to that site's mention of these prices: "The price sounds right, you get as much hybrid as you pay for."
[Source: Kicking Tires]