PORTLAND — Southwest Airlines will begin flying in mid-April between the Portland International Jetport and its hub at the Baltimore/Washington International Thurgood Marshall Airport.

Southwest, the nation’s largest domestic airline, will offer three weekday flights from Portland to Baltimore, and two flights each on Saturday and Sunday, according to the flight schedule on its website. One-way fares vary from $79 to $219.

Southwest will not serve any other cities directly from Portland. It will route customers to other destinations from its Baltimore hub.

Southwest, known for its low prices, “bags fly free” policy and superior customer service, will begin service out of Portland on April 14. AirTran, which Southwest acquired in May 2011, will end service on April 13. AirTran came to Portland in 2007.

Southwest confirmed in January that it would serve Portland. Its schedule and fares were not previously known.

Although AirTran serves the Portland-to-Baltimore route, the arrival of Southwest will mean more passengers flying with access to a broad network, said Paul Bradbury, director of the Portland International Jetport.

AirTran flies Boeing 717s, which carry 117 passengers. Southwest flies Boeing 737s, which carry 143 passengers. The increase in capacity will attract more passengers through the jetport, Bradbury said.

Also, Southwest has a broader national network.

“With Southwest, you have access to a much broader national network. The Southwest brand is also important to people. There are people who will come to the jetport specifically to fly Southwest,” Bradbury said. “Southwest fills a hole in the scope of airlines that we offer.”

Last year, the jetport completed a $75 million, 145,000-square-foot terminal expansion. It has been trying to lure new airlines. The jetport also has Air Canada, Delta Air Lines, JetBlue, United Airlines and U.S. Airways.

Although Southwest’s arrival in other airports has created fare wars in the past, Bradbury does not expect a big reaction at the jetport since AirTran and JetBlue already offer low costs and traditional airlines have become more competitive.