Passengers using them can obtain tickets at lowered prices upon boarding in card validators.
In some cases, the lowered prices have led fishermen to harvest more ocean fish in compensation.
Other airlines have since added flights or lowered prices, a phenomenon the airline industry calls the Southwest Effect.
"Once the city survived all of the lawsuits and moved forward with its network, the local incumbent lowered prices."
When Tiffany's lowered prices and quality and tried to reach out to the masses, they almost went bankrupt.
The letter cited the financial benefits of lowered prices at the pump but did not address environmental concerns.
The company made the changes quietly, by posting the lowered prices on its Web sites with no public announcement.
One purchase at a lowered price is a saving; it takes two to add up to savings.
With the lowered price, these efficient producers cannot compete.
But Barbara Boggs, the events planner, said she had not noticed any lowered prices.