The 2014 Mazda 3 has fuel economy ratings that are somewhat better than most cars in its class for base models, and significantly better than its competitive class if you opt for the higher-performance 's' model.
2014 Mazda 3 'i' models (with the 2.0-liter engine) return EPA ratings of 29 mpg city, 41 highway with the manual transmission, or 30/41 mpg with the automatic. Those are for the sedan; hatchback models lose 1 mpg on the highway. As for 's' models with the 2.5-liter engine, they're rated at 28/39 mpg for the Sedan and 27/37 for the hatchback. The top Grand Touring with the Tech package boosts the hatchback's mileage up to 28/38 mpg, however.
The Tech Package brings an i-ELOOP regenerative engine braking system and active grille shutters, along with several other active-safety extras. Simply put, i-ELOOP uses capacitors to run the alternator at its peak generation ability when decelerating and braking, to store energy that will then be used to run accessories (and run the alternator very lightly, with nearly no drag) when you're accelerating.
Both engines offer a very high (13:1) compression ratio, as well as direct injection and variable valve timing, and other measures that are aimed at saving fuel while maintaining responsiveness.
We managed more than 27 mpg over about 160 miles; and of that, about ten miles were crawling along in rush-hour gridlock and another 30 miles were driving very quick on mountain backroads, with the revs high. In relaxed daily commuting conditions you’ll easily top 30 mpg, we think, even with the larger 2.5-liter.