Expedia made four substantial acquisitions in 2015 worth a total of more than $6 billion, but which will be the most impactful?

To recap, Expedia acquired Travelocity for $280 million in January 2015, acquired an additional 25 percent and took a controlling stake in its joint venture with AirAsia for $94 million in March, added Orbitz Worldwide to its portfolio for $1.8 billion in September, and tacked on HomeAway for $3.9 billion in cash and stock in December.

That’s a combined price tag of around $6.074 billion.

Asked in November which of the recent acquisitions would be most impactful to Expedia, CFO Mark Okerstrom said he believes it will be Orbitz Worldwide.

“I think it’s going to be Orbitz,” Okerstrom said. “It’s a big scale business. It’s a business that was doing $12 billion in gross bookings, it was doing — I think this year — we’ve said on a run rate 135 and we think there are very meaningful synergies that we can add on top of that.”

It wasn’t clear if Okerstrom was considering the potential impact of the HomeAway acquisition when he addressed the issue in November; the HomeAway deal closed in December.

HomeAway notched $301.3 million in revenue during the first nine months of 2015, and by comparison Orbitz Worldwide generated $460 million in revenue in just the first six months of 2015.

But there is more than just the stark numbers to consider.

The integration of HomeAway into the Expedia platform could be a tricky one as Expedia plans to sell HomeAway’s vacation rentals on Expedia.com, Hotels.com and Venere.

Meanwhile, Expedia plans to begin uploading apartment rentals, especially in urban areas where HomeAway isn’t strong, and HomeAway will offer them on its own sites.

If the integration goes as Expedia and HomeAway envision then this merger can turn out to be transformational for both companies.

If that becomes the reality, then the Expedia acquisition of Orbitz may be evaluated in coming years as a mere footnote in Expedia’s timeline when compared with the HomeAway buy.

Photo Credit: A screenshot from HomeAway's 2015 video campaign about vacation rentals being the ideal accommodation for 'a whole vacation.' HomeAway