Airline network carriers as a group posted the smallest operating margin loss for any quarter since September 2007, and the airline industry as a whole reported an operating margin profit, according to a U.S. Department of Transportation report released Monday.

Operating margin measures profit or loss as a percentage of the airline’s total operating revenue.

The network group (a group of seven airlines featuring most of the industry’s largest carriers) reported a -0.5 percent loss margin, which continues a string of seven consecutive quarters with a loss for the group. The margin, however, was down considerably from the first quarter 2009 margin of loss at -4.0 percent and from the mark of -6.3 percent one year ago. As a group the network airlines reported a $111 million loss.

Four network airlines reported operating profit: United made $172 million, Northwest $143 million, US Airways $120 million and Alaska $31 million. Three others reported operating losses: Delta $159 million, Continental $159 million, and American $260 million.

The airline industry as a whole, however, improved operating margins in the second quarter to 1.2 percent ($361 million operating profit) from -2.4 percent in the first quarter. One year ago the industry as a whole had an operating margin of -4.5 percent.

Regional and low cost airlines, which reported operating margins of 7.2 percent and 7.0 percent respectively, buoyed the industry. Regional and low cost airlines operating margins were up considerably from a year ago when margins were 2.5 percent and 1.7 percent, respectively. Regional and low-cost airlines reported operating profit of $138 and $334 million, respectively.

Allegiant led low-cost airlines with a 23.8 percent operating margin, while five other airlines in the seven airline group also reported positive operating margins. Only Virgin America reported a negative operating margin of -8.4 percent during the second quarter.

Comair led regional airlines with a 16.2 percent operating margin, and five other airlines in the seven-airline group also reported positive operating margins. Only ExpressJet reported a negative operating margin of -6.1 percent during the second quarter. See the full report.