Most stable
Electricity and CNG showed the smallest variation. Electricity, which has cyclical price variations in summer compared to winter, had only a $1.04-GGE difference, ranging from $3.47 to $4.51 per GGE.
CNG had large price variations from 2005 to 2009, the DOE analysis says, but its price grew more stable after 2009. In this time period, its price ranged from $1.81 per GGE to $2.38 per GGE, or a 57-cent-per-GGE difference.