Calabrio, a Minneapolis-based maker of software that studies call-center interactions, is being purchased by well-known New York investment group KKR & Co.

Terms of the deal, announced Tuesday morning, were not disclosed. The Wall Street Journal, citing an unnamed person familiar with the deal, reported the transaction was valued at about $200 million.

“I couldn’t be happier,” Tom Goodmanson, Calabrio’s chief executive, said in an interview. “There’s a lot of great partners out there, but I think we really grabbed onto the best available to us.”

Calabrio is a fast-growing player in a business known as workforce optimization. It offers a variety of products that help companies identify what works when sales and service representatives are talking with customers and prospective customers on the phone, via e-mail and online.

Its estimated annual revenue is about $65 million, and the company has added 75 people this year to a staffing level of just more than 250.

Gartner, the technology consulting firm, late last year placed Calabrio in the same category as two of its larger rivals, Nice Systems and Verint Systems, for market leadership and completeness of its offerings. That recognition opened up the firm to a broader group of customers.

KKR plans to use Calabrio as a base to acquire several other technology companies that provide similar services.

“Calabrio has become one of the fastest-growing, quality companies in workforce optimization and customer engagement,” John Park, a KKR director, said in a statement. “With our partnership, we hope to accelerate the company’s growth even further.”

KKR, with $131 billion in assets under management, is one of the largest private investment firms in the country.

Earlier this year, it bought Mills Fleet Farm, the outdoor retail chain known for its giant stores and orange silos throughout the Upper Midwest. The purchase of Calabrio represents a relatively small deal for KKR, but it is a sign of the broader pressure on investment firms to find value at a time of record high stock prices and market caps.

It comes after Calabrio executives in recent months began to consider several options for the firm, including its first round of capital raising since 2007.

“We’ve built organically since then and were very fortunate we could grow the way we had,” Goodmanson said. “After nine years, it was time to refresh the capital table a little bit. That gave me the opportunity to find a partner who was interested in this sector.”

Calabrio was a spinoff from Spanlink Communications, now a unit of ConvergeOne, an Eagan-based customer technology services provider that is owned by another sizable investment firm, Clearlake Capital Group of Santa Monica, Calif.

The deal represents a big win for two Minnesota firms that provided the initial investment nine years ago for Calabrio — Split Rock Partners of Eden Prairie and BlueStream Ventures of Stillwater.

Michael Gorman, managing director at Split Rock, credited Goodmanson and the technology team at Calabrio for the company’s steady climb. A turning point came several years ago when the company decided to re-engineer its software and services to be “cloud-based,” or delivered via the internet, rather than installed and maintained in corporate networks through on-premise software.

“That was a very substantial undertaking and had great dividends in terms of costs and customer satisfaction,” Gorman said. “We knew that the cloud shift was underway and they did all of that in a very efficient manner.”