Expedia wasn’t content to finish the year with the trophies of former rivals Orbitz and Travelocity.

After the market closed today the increasingly giant online travel agency announced the acquisition of vacation rental giant HomeAway for $3.9 billion, increasing its acquisitions expenditures this year to north of $5.8 billion.

Along with its long-time rival Priceline Group and its former sister brand TripAdvisor, Expedia Inc. has been in a booking site arms race when it comes to acquisitions in the U.S. and abroad.

In their battle for online supremacy, Expedia and Priceline have opened their wallets and spent collectively more than $11.5 billion over the last two years.

The HomeAway purchase tops Priceline’s $2.6 billion acquisition of OpenTable in 2014 as the most valuable mergers and acquisitions deal in the booking market. Other hefty buys in travel technology include Oracle’s acquisition of hotel tech firm Micros for $5.3 billion and SAP’s Concur buy for $8.3 billion.

>> Related: First Interview: Expedia and HomeAway CEOs Talk Acquisition, Mistakes and Opportunities

Despite the flurry of activity in the booking sector, it may not be over any time soon.

“The overall travel category’s a trillion plus category,” Dara Khosrowshahi, Chief Executive Officer, Expedia, Inc., told Skift shortly after the announcement. “The alternative lodging category is 100 billion plus, so I think there’s room here for multiple winners.”

“I do think that Expedia Inc as a company becomes a tough competitor,” Khosrowshahi said, “But Booking.com and TripAdvisor have very strong road maps ahead of them, and I think that you’ve seen historically over the past five years, all three companies have been pretty successful. I don’t see that changing going forward.”

Below is a list of acquisitions in the online booking world since 2013. With the exception of Orbitz and HomeAway, companies are listed by the year in which the acquisition closed, not when it was announced.

Expedia Acquisitions

Company/YearPriceBackground
2015
HomeAway$3.9 billionread story
Orbitz$1.6 billionread story
Travelocity$280 millionread story
2014
Wotif$658 millionread story
Auto Escape$85 millionread story
2013
Trivago$632 million (62% stake)read story

Priceline Acquisitions

CompanyPriceBackground
2015
RocketMiles$20 millionread story
PriceMatchundisclosedread story
AS Digitalundisclosedread story
2014
OpenTable$2.6 billionread story
Buuteequndisclosedread story
Hotel Ninjasundisclosedread story
Qlika$3 millionread story
2013
Kayak$1.8 billionread story

TripAdvisor Acquisitions

Company/YearPriceBackground
2014
Viator$192 millionread story
VacationHomeRentalsundisclosedread story
Tripbodundisclosedread story
Lafourchetteundisclosedread story
My Tableundisclosedread story
Restopolisundisclosedread story
Iens$11 millionread story
2013
TinyPostundisclosedread story
Jetsetterundisclosedread story
CruiseWiseundisclosedread story
Niumbaundisclosedread story
GateGuruundisclosedread story
Oysterundisclosedread story