Traffic at McCarran International Airport fell 11.4 percent in June to 3.4 million arrivals and departures.
The numbers reflect the ongoing slump in Las Vegas visitation that has year-to-date arrivals and departures down 11.8 percent to 20.2 million.
US Airways led the decline, falling from 679,956 to 422,411 arrivals and departures for the month, a dip of 37.9 percent.
Southwest, which flies more people to Las Vegas than any other airline, flew 1.4 million arrivals and departures, a decline of 4.2 percent.
United, the third-largest carrier at McCarran behind Southwest and US Airways, was down 4.2 percent to 247,690 arrivals and departures.
American, the fourth-largest carrier, increased arrivals and departures 15.5 percent to 194,482.
The American increase comes as the airline changed the mix of aircraft to reduce the ratio of MD-80s in favor of adding 737s and 757s, which have more seats.
Delta also posted an increase, boosting its arrivals and departures 1.3 percent to 189,160 for the month.
Other significant carriers to post increases at McCarran were Las Vegas-based Allegiant and trendy newcomer Virgin America.
Allegiant grew Las Vegas 11.2 percent to 182,620 arrivals and departures and Virgin increased traffic 5.2 percent to 32,260 arrivals and departures.
For the year, Southwest has flown 7.7 million arrivals and departures, off 5.1 percent from the 2008 pace.
US Airways is down 33 percent from the 2008 pace with 2.6 million arrivals and departures through June.
Contact reporter Benjamin Spillman at email@example.com or 702-477-3861.