Boston private equity firm TA Associates has invested in Plusgrade, a revenue service for the travel industry, for an undisclosed amount.

Plusgrade, based in New York and Montreal, aims to help airlines manage and optimize revenue generated from seat upgrades and other services. The company’s software is used by more than 35 airlines.

An estimated $49.9 billion, or 6.7 percent of global airline revenue came from ancillary revenue streams (including premium seat assignments, early boarding, checked baggage, etc.) in 2014, an increase from $22.6 billion in 2010, according to consulting firm IdeaWorksCo.

There have been several other travel-related M&A deals recently. In May, IBM (NYSE: IBM) invested in WayBlazer, a travel search operation, and Sabre Corp. (Nasdaq: SABR) agreed to buy the rest of travel service Abacus International for $411 million. Thoma Bravo’s $930 million purchase cloud-based travel software business TravelClick was named Mergers & Acquisitions M&A Mid-Market Deal of the Year for 2014.

TA Associates has made several investments recently. Earlier in August, the firm invested in CCRM, a network of fertility treatment clinics.  TA portfolio company Nintex acquired document-generation software Drawloop Technologies Inc. in July. 

Stikeman Elliott LLP and Goodwin Procter LLP provided legal advice to TA. Davies Ward Phillips & Vineberg LLP and Greenberg Traurig LLP were Plusgrade's legal counsel.