Both Fujifilm X10 and Canon S120 have 12.0 MP resolution sensors but Fujifilm X10's sensor is 2/3" (8.8 x 6.6 mm ) and Canon S120's sensor is 1/1.7" (7.44 x 5.58 mm ).
Since Fujifilm X10's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Canon S120.
Below you can see the X10 and S120 sensor size comparison.
As seen above, Fujifilm X10 has a 1.4x Larger sensor area than Canon S120. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Fujifilm X10 and Canon S120 sensors have been tested by DxO and the results show that S120 has a better overall score of 56, 6 points higher compared to X10's score of 50.