Travel sites keep upping their competitive features, and Hipmunk now has more funding to reach new heights of de-agonized travel planning.

On Friday, the San Francisco-based company – which prides itself on a transparently easy interface, cross-platform consistency and mobile-only specials – said that it has landed a $20 million Series C funding round, led by Oak Investment Partners. Its Series B funding of $15 million was completed in June of 2012, on top of $5 million total in previous Series A and seed funding.

“We’ve got roughly 20 very talented engineers,” co-founder and CEO Adam Goldstein told VentureBeat, “and we’ll be bringing in another 15 to 20 to help expand our presence [across devices].”

He also said the funding will help to expand partnerships, such as the “pioneering partnerships with Airbnb and HomeAway, [and] to reach the broadest possible audiences on mobile.” Goldstein said mobile has always been a focus of Hipmunk, as it was “the first whole services site that came of age in the age of mobile.”

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“Some people have asked: are you going to invest in TV ads?” The answer, he said, is no.

The board of directors will get a new member, Ren Riley, an Oak Investment general partner. Oak has also backed travel site Kayak, in addition to the Huffington Post, Thrillist Media Group, and Bleacher Report. Riley noted that Hipmunk, since its founding in the summer of 2010, “has developed an energetic user base, industry-leading cross-platform integration, and key partnerships.”

The site was started by Goldstein, then-recently graduated from MIT, and Steve Huffman, University of Virginia graduate and Reddit cofounder, in an effort to make travel planning less agonizing.

“When I was at M.I.T.,” Goldstein told us, “I was captain of the debate team and one of the most frustrating experiences was booking travel.” The day after graduation, he said, he moved to San Francisco to work on removing that frustration.

The site compares offerings from travel sites to present the best deal for commercial flights, trains, charter flights, hotels, and through Airbnb and HomeAway, vacation rentals. An iOS app was launched in early 2011, and an Android version in early 2012.

Aside from ease-of-use, the site promotes its mobile-only hotel deals that can be as much as 60 percent off, and the recently launched Hipmunk Anywhere, which maintains search results across devices for logged-in users.

Although speed and anti-agony ease-of-use are its key intended differentiators, the company has hit a few bumps that it has had to work through. In the fall of 2012, for instance, it completely rebuilt its hotels product following reports that it was fairly slow and hard to use. Previously, its focus has been on flights.

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