The 9th generation 2012 Honda Civic was previewed as a concept, in both sedan and coupe body styles at this year’s NAIAS, and now the Japanese company has releases photos and details with the production model which will hit the market in spring.
Besides the Si, the  2012 Honda Civic lineup has been extended with two now models, and these are the Civic HF and Civic Hybrid, which both promise fuel consumption figures above 40 mpg on the highway.
The 2012 Honda Civic HF is equipped with a 1.8-litre i-VTEC engine delivering 140 HP through a five-speed automatic gearbox, and will be the most fuel efficient gasoline power model in the entire lineup.
On the 2012 Honda Civic Hybrid power is get extracted from a 110 HP 1.5-litre i-VTEC 4-cylinder engine mated to an electric motor and backed by a lithium-ion battery. In this case power is sent to the wheels via a Continuously Variable Transmission (CVT) transmission and estimated consumption is 45 mpg/combined cycle.
Both the 2012 Honda Civic Hybrid and HF feature the ECO Assist technology.
On the 2012 Honda Civic Si, the automaker has fitted a 2.4-litre i-VTECH 4-cylinder unit producing 200 HP and 170 lb-ft of torque. This version comes with a 6-speed manual gearbox, and is expected to deliver 31 mpg highway. 
Honda press release :
Featuring the widest array of engine choices available in its class, the 2012 Civic is designed to even better meet the diverse needs of the compact-vehicle buyer when it launches this spring. The entire redesigned ninth-generation Civic lineup will become more fuel efficient with two models – the all-new Civic HF and the Civic Hybrid – each delivering fuel economy estimates of more than 40 mpg on the highway.
Built on the tradition of Honda fuel efficiency, the economical Civic HF model will be the most fuel-efficient gasoline-only powered Civic in the lineup when it launches this spring. Equipped with a 1.8-liter i-VTEC engine, the Civic HF is targeted to earn EPA-estimated fuel economy1 of 41 mpg on the highway. The 2012 Civic Hybrid, which will be outfitted for the first time with a lithium-ion battery and a larger 1.5-liter i-VTEC engine, is expected to achieve an EPA-estimated city/highway combined fuel economy1 of 45 mpg, an improvement of 4 mpg compared to the current Civic Hybrid. Both the Civic HF and Civic Hybrid models will be equipped with aerodynamic components for improved efficiency and Honda ECO Assist™ technology, an innovation that can enhance efficient vehicle operation while providing feedback to promote more efficient individual driving styles.
"The Civic is the only model in the industry that can deliver on all fronts – fuel economy, sporty performance, smart packaging, alternative fuel and long-term value," said John Mendel, executive vice president of sales for American Honda Motor Co.,Inc. "For the ninth-generation Civic, we are emphasizing improved fuel economy across the board, from the hybrid sedan to the sporty Si model."
In addition to the Civic HF and Civic Hybrid models, the Civic Sedan, Civic Coupe and Civic GX Natural Gas models are also estimated to achieve improved fuel economy compared to the current models. The Civic Sedan and Civic Coupe achieve an EPA-estimated fuel economy2 of 39 mpg on the highway, an improvement of 3 mpg when compared to the current model. The Civic Natural Gas vehicle is anticipated to earn a 7 percent improvement in fuel economy compared to the current model. The Civic Sedan, Civic Coupe and Civic Natural Gas models will all be equipped with the Honda ECO Assist technology.
Along with improved fuel economy, the new Civic lineup also delivers more performance, particularly with the Civic Si. The Civic Si sedan and coupe models will be equipped with a larger, more powerful 2.4-liter engine as well as a new 6-speed manual transmission. The new engine is anticipated to deliver 200 horsepower with 170 ft-lb of torque. Even with the larger engine and a 22 percent increase in torque, Civic Si is targeted to achieve an EPA-estimated highway fuel economy1 of 31 mpg; an increase of 2 mpg when compared to the current model.
The 2012 Civic lineup includes a sedan and a coupe with conventional gasoline models, a new "HF" high fuel economy version, two sporty "Si" performance versions, along with one hybrid and a natural gas alternative-fuel variant.
Additional information on the new 2012 Civic will be announced closer to the on-sale date. For more information on the current Civic and other Honda models, please visit www.hondanews.com.
Civic HF, Sedan, Coupe and Natural Gas Specifications
    * 140 horsepower, 1.8-liter i-VTEC™ 4-cylinder engine
    * 5-speed automatic transmission
    * ECO Assist technology
    * EPA-estimated Civic HF highway fuel economy: 41 mpg
    * EPA-estimated Civic Sedan and Civic Coupe highway fuel economy: 39 mpg
Civic Hybrid Specifications
    * 110 horsepower, 1.5-liter i-VTEC™ 4-cylinder engine (combined gasoline + electric)
    * Continuously Variable Transmission (CVT)
    * Lithium-ion battery
    * ECO Assist technology
    * EPA-estimated Civic Hybrid city/highway combined fuel economy: 45 mpg
Civic Si Specifications
    * 200 horsepower and 170 lb-ft, 2.4-liter i-VTEC™ 4-cylinder engine
    * 6-speed manual transmission
    * EPA-estimated Civic Si highway fuel economy: 31 mpg
1Preliminary EPA mileage estimates determined by Honda. Final EPA mileage estimates not available at the time of printing. Use for comparison purposes only. Your actual mileage will vary depending on how you drive and maintain your vehicle.
2Based on 2012 EPA mileage estimates. Use for comparison purposes only. Do not compare to models before 2008. Your actual mileage will vary depending on how you drive and maintain your vehicle.

Source: Honda