RANKED: The hottest US pre-IPO ad tech startups of 2015

Tomer Bar Zeev IronSourceLinkedIn/Tomer Bar ZeevTomer Bar Zeev, co-founder and CEO of IronSource.

The majority of ad tech companies on the public markets may have fared badly in recent months, but behind the scenes there are some seriously interesting pre-IPO ad tech startups

This ranking looks at the hotter companies subject to IPO (or at least big exit deal) rumours right now. Our data comes from CrunchBase, LinkedIn, our own reporting, and that of other business publications. We’ve tried to rank them by revenues, but have also taken into account headcounts, venture funding, and recent news and whispers.

See our methodology at the end.

27. Sharethrough: The largest 'native' ad exchange

Sharethrough co-founder and CEO Dan Greenberg

CEO: Dan Greenberg

Employees: 160

Estimated revenues: We believe around $US30-$US40 million, net.

Total venture funding: $US28 million

Comment: The company operates a 'native' ad exchange and is targeting annual revenue of $US100 million by the end of the year. It is profitable.

26. Taykey: Supported by Google's Eric Schmidt

Taykey CEO and founder Amit Avner.

CEO: Amit Avner

Employees: 90

Estimated revenues: We estimate around $US30 million

Total funding to date: $US32 million

Comment: Taykey's latest funding round was led by Eric Schmidt's venture arm Innovation Endeavours. The company, which plugs its software into more than 50,000 social sources -- such as YouTube, DailyMotion, and BuzzFeed -- to provide insights to marketers on what is trending now for their desired audiences says it has grown revenue by 600% since January 2013. Avner told us he expects this triple digit growth to continue into 2015.

25. Socialbakers: A well-respected young CEO and huge client base

Socialbakers CEO Jan Rezab.

CEO: Jan Rezab

Employees: 330

Estimated revenues: Greater than $US30 million.

Total venture funding: $US34 million

Comment: Rezab was named one of Forbes' '30 under 30' in marketing and advertising earlier this year. His social media management and analytics company has more than 2,700 clients, and is considering the possibility of going public. Rezab says the Prague-based company has doubled in size every year 'for a while now,' and this year it is concentrating its efforts on US expansion.

24. Unruly: Benefiting from the shift of ad dollars from TV to digital video

Unruly CEO Scott Button.

CEO: Scott Button

Employees: 190

Estimated revenues: $US42 million in 2014

Total venture funding: $US25 million

Comment: The London-based video ad tech company increased revenue by 23% year on year, helped by the continued shift of ad dollars from TV to digital. Last year Unruly opened an APAC HQ in Singapore, and it launched new products including a programmatic media trading platform to guarantee the viewability of video ads, a skippable pre-roll ad format, and a native in-feed format.

22. Kenshoo: Plans to IPO in the US in 2015

Kenshoo CEO Yoav Izhar-Prato

CEO: Yoav Izhar-Prato

Employees: 500

Estimated revenues: ~$US50 million to $US100 million in 2014.

Total venture funding: $US49.7 million

Comment: The Tel Aviv-based company handles tens of billions of dollars worth of search, local, and social media advertising. It is one of Google's biggest clients in terms of buying shopping ads. Its chief executive said it is planning on a US IPO in 2015, that could value the company at $US750 million, adding in an interview with Bloomberg 'it's healthy for us to be a public company.'

21. Tapjoy: App developers' best friend

Tapjoy CEO Steve Wadsworth.

CEO: Steve Wadsworth

Employees: 275

Estimated revenues: ~$US100 million, around the same as in 2011.

Total venture funding: $US65 million

Comment: Tapjoy helps app developers make money through its advertising platform. Its software is embedded in more than 270,000 apps and it reaches more than 520 million monthly active users. Last year Tapjoy acquired Korean startup 5Rocks, as part of its aims to become a one-stop-shop for mobile app developers.

20. Kargo: $0 venture funding

Kargo CEO Harry Kargman.

CEO: Harry Kargman

Employees: 120

Estimated revenues: We estimate greater than $US80 million.

Total venture funding: $US0

Comment: Unusually for an ad tech company, Kargo has raised zero venture funding to date, which places it in a prime position for outside investor interest. Kargo has built its business on a publisher platform that combines content with native brand advertising from the likes of McDonald's, AT&T, Unilever -- 150 customers in total. It began trading on mobile viewability last year, guaranteeing advertisers 80% in-view ads or their money back.

18. Sprinklr: Hugely ambitious and a likely IPO candidate.

Spriklr CEO Ragy Thomas.

CEO: Ragy Thomas

Employees: 800+

Estimated revenues: Believed to be aiming for $US100 million this year

Total venture funding: $US123.5 million

Comments: Last year Sprinklr -- an enterprise social media management company -- acquired TBG Digital, one of Facebook's largest ad-buying clients. Combined, the companies process more than $US100 million in annual media spend for clients including Microsoft, Vodafone, Intel, and Dell. Sprinklr has also acquired four companies since. A source told Business Insider in April 2014 that Sprinklr was planning an IPO, and CEO Thomas is known to want to build a '$US10 billion company.'

17. Centro: Helping smaller advertisers get into programmatic

Centro CEO Shawn Riegsecker

CEO: Shawn Riegsecker

Employees: 600

Estimated revenues: Projected ~$US100 million this year, according to industry sources

Total venture funding: $US22.5 million

Comment: Centro's advertising platform is used by advertising agencies to manage the workflow of their digital campaigns. The company launched a demand-side platform in May, which claims to be mobile-first. The Centro DSP was specifically designed to meet the needs of smaller advertisers that find it hard to develop relationships with the bigger demand-side platforms due to minimum spends and set-up fees. Centro claims to have 2,500 customers and sources tell us the company is looking to raise more funding this year.

16. DataXu: Powered by MIT scientists, and aiming to solve the cross-device issue

DataXu CEO Mike Baker.

CEO: Mike Baker

Employees: 300

Estimated revenues: $US118.4 million in 2013

Total venture funding: $US55.8 million

Comment: In March DataXu launched a new platform called OneView that aims to solve one of marketers' biggest mobile headaches: targeting and measuring consumers as they switch from device to device. The company, which was founded by MIT astronautics and aeronautics scientists, who wrote the programs that guided NASA's Mars mission plans, now has over 400 customers including Vodafone, Ford, and General Mills. Baker claims the company grew revenue by 50% year over year in 2014.

15. xAd: Location-focused and making key hires

xAd CEO Dipanshu Sharma.

CEO: Dipanshu Sharma

Employees: 200+

Estimated revenues: We estimate around $US130 million.

Total venture funding: $US74 million

Comment: The location-focused advertising network claims to allow nearly 1 million advertisers to reach 300 million unique people each month. The company itself is growing worldwide, having recently announced it had hired agency veteran Brand Starkoff to lead its US sales team, and expanded into Spain and Italy. Prior to that it has also poached executives from Twitter, Facebook, Google, and Posterscope this year. Because the company is laser-focused on location, we predict it is more likely a M&A target than an IPO candidate.

14. PubMatic: All signs point towards solid growth

PubMatic CEO Rajeev Goel.

CEO: Rajeev Goel

Employees: ~600

Revenues: ~$US130 million revenue run rate in 2014

Total venture funding: $US63 million

Comments: PubMatic said its revenue increased 90% year on year in 2014, while 'doubling its rate of profitability.' Last year the company expanded into new markets including Japan, Singapore, Italy, Brazil, the Middle East, and North Africa.

13. AdRoll: Lots of ex-Googlers, and working with Apple

AdRoll CEO Aaron Bell.

CEO: Aaron Bell

Employees: 494

Revenues: ~$US150 million annual run-rate

Total venture funding: $US89 million

Comment: AdRoll is one of the partners of Apple's move to bring programmatic ad buying to its iAd platform for the first time. More than 15,000 advertisers use its retargeting platform worldwide. And lots of ex-Googlers work there.

12. Collective: Its sell is transparency, one of the biggest issues in ad tech right now.

Joe Apprendi, CEO of Collective.

CEO: Joe Apprendi

Employees: 400

Revenue: ~$US200 million

Total venture funding: $US86.4 million

Comment: Apprendi suggested to Business Insider recently that the company was not in the market for an IPO: 'Being well-capitalised and private is better than 'open kimono' right now,' referring to the performance of the large ad tech companies on the public market. Collective prides itself on offering clients transparency about how their money is spent, the cost of inventory bought, and the results they get. Last year it divested its dynamic creative optimization tech -- branded Ensemble -- to Adobe.

11. Quantcast: High-profile recent hires and a clear focus

Quantcast CEO Konrad Feldman

CEO: Konrad Feldman

Employees: 650

Estimated revenues: We estimate a ~$US200 million net revenue annual run rate

Total venture funding: $US61.2 million

Comment: Quantcast hired a new CFO, and its first SVP of engineering in December -- big hires from The Weather Company and Amazon, respectively. Back in October it made a big acquisition: Struq, a London-based cross-device retargeting company. Quantcast is focusing its efforts on programmatic ads, and it keeps on growing, all while staying EBITDA positive, we are told.

10. Undertone: Has taken the leap into programmatic and has a differentiated offer by focusing on creative

Undertone CEO Corey Ferengul.

CEO: Corey Ferengul

Employees: 343

Estimated revenues: ~$US200 million

Total venture funding: $US40 million.

Comment: Undertone focuses its efforts on the creative, media, and tech that allows advertisers to create video ads that work across all different sizes of screen. It recently acquired a programmatic company called Upfront, and in April began selling its splashy video ad format programmatically.

9. Mediaocean: Expanding into programmatic TV

MediaOcean CEO Bill Wise.

CEO: Bill Wise

Employees: 800

Estimated revenues: Owler estimates more than $US233 million

Total venture funding: $US40.5 million

Comment: Mediaocean runs $US100 billion in media spend through its platforms for more than 80,000 advertisers. It's one of the first partners to Facebook's Atlas ad platform, and recently it extended its platform to cover TV advertising through a partnership with iSpot.tv. The company was reportedly worth $US1.5 billion back in 2012.

8. Outbrain: An IPO is imminent

Outbrain CEO Yaron Galai.

CEO: Yaron Galai

Employees: 400

Estimated revenues: $US260 million in 2014, according to AmigoBulls

Total venture funding: $US99 million

Comment: The content recommendation company has been expected to file an IPO 'imminently' since last year. But in November the company filed confidentially with the US Securities and Exchange Commission, seeking preliminary approval to list on the Nasdaq, according to the Wall Street Journal. The WSJ's sources say Outbrain is expected to seek a valuation of around $US1 billion. But nothing else related to the IPO has surfaced publicly since.

7. InMobi: Rumoured to have been subject of an acquisition bid by Google

InMobi chief Naveen Tewari

CEO: Naveen Tewari

Employees: 900

Estimated revenues: $US400 million, according to The Economic Times of India.

Total funding to date: $US220.6 million

Comment: Rumours emerged back in March that InMobi was subject to an acquisition offer from Google. Tewari quickly dismissed these rumours saying 'there is no reason to sell,' although he has long-hinted that the company may be preparing for an IPO. However, the company has struggled recently to raise interest from investors beyond Japanese internet company SoftBank, and is yet to turn a profit, according to sources.

6. Videology: A specialist in the fastest-growing area of online advertising

Scott Ferber, chairman and CEO of Videology.

CEO: Scott Ferber

Employees: 350

Estimated revenues: ~$US300 million in 2014

Total venture funding: $US134.2 million

Comment: Ferber has previously told Business Insider the company was 'preparing' for an IPO in 2015, but the market has changed a lot since March 2014, so it may not happen. The video ad tech company said earlier this month it had seen programmatic mobile video campaigns jump 81% in Q1 -- one of the rising trends in advertising.

5. MediaMath: The industry's favourite

MediaMath CEO Joe Zawadzki.

CEO: Joe Zawadzki

Employees: 600+

Estimated revenues: $US300 million to $US400 million (according to our estimates.)

Total venture funding: $US207.5 million

Comment: Last year we asked a bunch of executives which company they thought was the hottest ad tech startup, and MediaMath's name kept coming up. The company claims to be profitable and said sales last year reached $US311 million. In October it acquired social advertising firm Upcast, building out its ad tech stack to social channels like Facebook.

4. Taboola: Expanding internationally at a great clip

Taboola Founder and CEO Adam Singolda.

CEO: Adam Singolda

Employees: 270

Estimated revenues: $US300 million+ annual revenue run-rate.

Total venture funding: $US117+ million

Comment: Singolda tells Business Insider that we shouldn't expect an IPO any time soon. Instead the company wants to expand into new geographies and keep growing its market share. Taboola's content discovery platform is huge. Its sponsored content reaches more desktop users in the US than Facebook, Yahoo, and YouTube, according to comScore's syndicated ad rankings. It's expanding globally too, having recently signed investment and partnership deals with Yahoo Japan and Baidu in China.

3. IronSource: An Israeli unicorn

IronSource CEO Tomer Bar Zeev.

CEO: Tomer Bar Zeev

Employees: 500

Estimated revenues: ~$US350 million gross revenue run rate

Total venture funding: $US105 million

Comment: IronSource is a Tel Aviv-based mobile ad tech company, offering user acquisition, conversion, monetisation, analytics, and optimization tools. It announced the opening of a London office in April to better serve its European customers, and it is strongly tipped to go public late this year or early next, with a valuation of more than $US1 billion.

2. AppNexus: Struck a mega partnership with WPP that will secure long-term ad revenue

AppNexus CEO Brian O'Kelley.

CEO: Brian O'Kelley

Employees: 920

Estimated revenues: We estimate greater than $US250 million and maybe as much as $US300 million

Total venture funding: $US250 million

Comment: In September last year WPP, the world's largest ad agency holding company, announced it was investing $US25 million in AppNexus, taking its stake from 1% up to 15%. The deal basically saw WPP commit to funelling its clients' ad money through AppNexus, securing future revenue. In addition, AppNexus also acquired WPP's profitable Xaxis for Publishers unit (a product that serves ads for website publishers) as part of the deal. In March AppNexus acquired analytics company Yieldex for $US100 million in cash and stock to further grow out its ad tech stack.

Methodology: How this list is ranked

We looked at the following factors when we adjust our rankings and publish a new version of the list:

Revenues: This is the single most important factor in our ranking. Companies with robust businesses have revenues they can talk about in dollars (not blind percentage 'growth' claims.) Companies that are modest about their revenues are usually modest for good reason.

Total employees: Companies tend to hire more people because they're handling more business. Headcount is a good proxy for growth -- although having too many employees can drive down margins.

Funding: Investors tend to want their money back. So companies that have taken a lot of investment funding are under greater pressure to IPO than those that have not.

Reputation: It's great that some companies like to grow quietly without the distraction of the media spotlight -- we're happy to ignore them.

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