Charleston International Airport's airfares have been descending steadily in recent years with the arrival of new low-cost carriers.

But one online travel service places the fares really low. So low, in fact, they landed as the most inexpensive in the nation, according to cheapflights.com.

The travel service says the price of a round-trip ticket in June from Charleston International to popular destinations cost $191, the cheapest in the U.S., rising 30 notches over last year's ranking.

That's in stark contrast to a report from the U.S Department of Transportation, which ranks fares at the top 100 airports in the country based on number of passengers.

In the fourth quarter 2013 rankings by the DOT, the latest statistics available, Charleston's airfares cost $397 for a round-trip domestic flight and the airport ranks 40th highest. That rate is down 31.3 percent from 2000, when it averaged $578.

The cheapflights.com report also said Myrtle Beach's airport ranked ninth with an airfare of $287, while Greenville-Spartanburg's airport dropped 16 spots to 62nd with an average rate of $409.

The DOT fare for Greenville-Spartanburg was $372 for the fourth quarter of 2013. Myrtle Beach's airport does not rank on the DOT top 100 list.

The online travel site uses a snapshot of people searching for flights during June. One possible explanation for the disparity is that JetBlue Airways starting serving Reagan National Airport near Washington, D.C., last month with introductory discount rates. Some local airlines trimmed rates as a result.

When asked about the difference in prices between the DOT airfare numbers and cheapflights, spokeswoman Dalia Blumenthal said the online service looked at different data and a different time frame.

"The Department of Transportation looked at all domestic flights for a quarter at the end of last year while we picked a selection of popular routes and looked at them over the month of June," she said. "Timing might be key as JetBlue's growing presence in the market is likely having a continued downward effect on pricing, especially on flights to key major markets and hubs for longer haul travel.

"Having Southwest in the mix most likely adds to the pricing pressure for many popular routes as well. Because the DOT looked at all flights (not just ones to major or popular destinations), that discount or budget airline effect may not have been felt as keenly," Blumenthal said.

Charleston airport officials welcomed the report.

"We're excited to be on this list because this is great news for passengers," said Paul Campbell, director of airports for the Charleston County Aviation Authority. "Charleston's popularity with visitors continues to grow, and now they can find affordable ways to visit our great community."

Charleston International is served by Delta Air Lines, American, US Airways and United, as well as low-cost providers JetBlue and Southwest.

"We are fortunate to have the major airlines at the airport, along with JetBlue and Southwest. Fares are competitive, and that's good for passengers," Campbell said.

Cheapflights.com said its rankings provide travelers with a way to see how nearby airports measure up and potentially expand departure or arrival options during a flight search.

"These rankings fluctuate year to year and prices can change frequently (and dramatically) along routes, but as always, there are a few key takeaways: Do your research, check out all your options and, if you can, be flexible with your travel plans - it could yield significant savings," cheapflights.com said in a statement.

Reach Warren L. Wise at 937-5524 or twitter.com/warrenlancewise.