SkyActiv is a series of technologies developed by Mazda

Mazda

is a Japanese automotive manufacturer based in Fuchū, Aki District, Hiroshima Prefecture, Japan.In 2007, Mazda produced almost 1.3 million vehicles for global sales...

 which increases fuel efficiency and engine output. Among some of its technologies include a new gasoline engine that uses diesel-like compression ratios to improve fuel economy, a new automated transmission which combines a tradition automatic's torque converter with a dual-clutch, and a lightweight body design.

• Skyactiv-G is a 2-liter engine displacement
  Engine displacement
  Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...
  
  , 4-cylinder, gasoline engine which is according to Mazda more fuel effective than their earlier comparable engines. By using this engine in the 2012 version of the Mazda3, they claim that with an automatic transmission
  Automatic transmission
  An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...
  
  , they improved fuel economy
  Fuel economy in automobiles
  Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
  
   from 23 mpg
  MPG
  MPG or mpg may refer to:*.mpg, one of a number of file extensions for MPEG-1 or MPEG-2 audio and video compression*General Motors Milford Proving Ground*Havas Media, formerly known as Media Planning Group, a media division of Havas...
  
  to 28 mpg in town, and from 33 mpg to 40 mpg on the highway compared to the 2011 model.