certified CNG switchable to gas kits for:
 

2000
3.8L, 3.5L, 3.4L
GRAND PRIX, IMPALA, LUMINA/MONTE
CARLO, REGAL, BONNEVILLE, CAMARO,
FIREBIRD/TRANS AM, LESABRE, PARK
AVE, CENTURY, ALERO, GRAND AM,
MALIBU, CAMERO, INTRIGUE, AURORA

2008
2.4L, 2.2L
SATURN AURA, PONTIAC G6, CHEVROLET
MALIBU, CHEVROLET COBALT, PONTIAC
G5, CHEVROLET COBALT XFE, PONTIAC
G5 XFE, CHEVROLET CLASSIC

here's link to page: http://www.ngvamerica.org/pdfs/Avail...nd_Engines.pdf

These were the smallest engine sizes I could find. As long as the kit/ installation is approved, one can be put on any vehicle anyway though. The above kits are ready to go though.

There are certified CNG US kits for many other lower power cars though they're newer, and also the lowest is a 2.0L(for 2009 version Ford Focus). As far as I've found.

Should we discuss whether this is an "eco" mod or not?