For its size, the 2014 Kia Azera isn't a particularly fuel-efficient vehicle; it's surpassed by powertrains like the EcoBoost four in the Ford Taurus (22/32 mpg), as well as the hybrid powertrain that delivers 40 mpg Combined in the Toyota Avalon Hybrid.
It's also worth noting that the Hyundai Azera, curiously, gets 20/29 mpg ratings with essentially the same engine and transmission. In a 140-mile drive of the Cadenza we saw about 21 mpg, with no passengers aboard, and about two thirds of that on the highway and on rural two-laners; that's within a mpg of what we've observed in the Azera.
The Cadenza's fuel economy ratings are just 19 mpg city, 28 highway. But, as Kia notes, the V-6 in the Cadenza is designed to run on regular unleaded gasoline.