WEX Inc., the South Portland-based payment technology company, on Thursday said it will acquire a health care billing software company in Nebraska for $80 million.

The acquisition marks another milestone in the company’s evolution from a provider of payment services for businesses with vehicle fleets to a large player in the travel and health care payment technology space.

WEX expects its acquisition of Omaha-based Benaissance, which has been approved by both companies’ boards but is subject to regulatory approvals, to close in the fourth quarter of 2015.

Founded in 2003, Benaissance offers cloud-based financial management software for health benefit administrators and health plans. It had 2014 revenue of $13.3 million, a 398 percent increase over the previous three years, and roughly 100 employees, according to Inc. magazine, which placed the company on its list of the country’s 5,000 fastest-growing private companies for the past two years.

“The acquisition of Benaissance builds on the success we have already had in the health care space by allowing us to provide an expanded and differentiated payments solution,” said Melissa Smith, WEX’s CEO, in a statement. She said the acquisition will enhance WEX’s market opportunities, improve customer loyalty and company profits.

Last summer, WEX made its largest acquisition in its history when it acquired another health care payment technology company, Fargo, North Dakota-based Evolution1, for $532.5 million in cash. Evolution1 develops software that employers can use to make and track payments to health care providers, such as from an employee’s flexible spending account.

On Thursday, WEX said it would integrate Benaissance’s services into its existing Evolution1 platform.

The acquisition announcement gave WEX’s stock a slight boost. On Thursday, the stock closed at $92.30 a share, 1.5 percent increase over the day’s opening price. However, the company’s stock has fallen over the past year from a 52-week high of $119.11 reached last November.