Clothes dryers don't come with Energy Star labeling since there's little difference in energy use between models of the same type, so when you're shopping for a gas verses electric dryer, you'll need to consider two factors: the up-front cost of the appliance itself, and how much it'll cost to operate over the years you use it.
Gas clothes dryers generally cost more, but can save you about 50 percent in annual dryer energy costs over electric models. And new dryers' moisture sensors can help you save another 15 percent by shutting of the unit as soon as clothes are dry.
If you're still not sure of what your savings will be, compare the energy factors of gas verses electric dryers. This is a measure of efficiency by pounds of clothing per kilowatt-hour of electricity (applied to gas-powered appliances as well). For your reference, a standard-capacity electric dryer will have a minimum energy factor of 3.01, while an equivalent gas-powered unit will have a minimum energy factor of 2.67.