NBC NATIONAL NEWS — Southwest Airlines has raised its airfares on most domestic flights by $10 round trip and other airlines are doing the same.

When southwest raises fares, other airlines typically follow.

This time, American Airlines, Delta Air Lines, and US Airways have matched the increase.

A Southwest spokeswoman says the increase is to cover operating costs.

This is the second airfare increase of the year.

Just last month, airlines raised fares by $10 each way on long flights.