The global digital advertising market grew 21% to $88 billion in 2017, according to the IAB Internet Advertising Revenue Report released Thursday and conducted by PwC.

But because Facebook and Google account for 90% of that growth, according to Pivotal Research analyst Brian Wieser, others shouldn’t benchmark their own growth rates against the industry average.

While Facebook and Google may contribute to most of the revenue growth, the IAB reported that the top 10 companies on its list contributed 68-75% of overall revenue. Only three companies in the top 10 in 2008 remain on the list today. However, the IAB and PwC couldn’t reveal who those members were in order to maintain the confidentiality of those who submitted information for the report.

Additionally, search advertising ceded market share to video advertising.

Despite growing 18% to $40.6 billion, search went from 48% to 46% of the market, while video advertising grew 33% to $11.9 billion.

Audio advertising also posted incredible growth, rising 29% to $1.6 billion. The category remains a beansprout, though, accounting for just 2% of the market.

The IAB report identified two major factors driving growth: self-serve platforms that allow small businesses to advertise with ease on the internet, and the rise of online startups that use these self-serve platforms to sell products directly to consumers.

Facebook and Google capture the majority of that growth because they excel at serving those two sets of customers.

“Our discussions with leading industry participants suggest that a lack of self-service tools, prohibitive minimum advertising buys, and reliance on direct sales or programmatic platforms that do not cater to small businesses may be restricting the number of advertisers who are aware of and active on all but the most popular platforms,” the report stated.

Mobile accounted for 56.7% of all the digital advertising, growing 36.2% last year. But the report cautioned that mobile growth rates are starting to decline after an epic rise. Last year, for example, mobile grew 77%, and mobile doubled every year for the first few years the IAB started tracking mobile advertising, starting in 2011.

The report also broke out social media advertising, which accounted for $1 of every $4 spent on digital advertising. Ads on social media grew 36% to $22.2 billion year over year, far outpacing the overall growth rate in digital.