Digital work accounted for a record 41.3% of U.S. agency revenue in 2015, reflecting how the ad industry is adapting to the world of digital marketing, according to a new report from Advertising Age.

Digital revenue for U.S. agencies surged 13.5% in 2015 to $19.3 billion, including digital work for all agency types from ad agencies and media agencies to public relations agencies and digital pure-play agencies, according to Ad Age's annual Agency Report, released today.

Internet-related work drove industry growth as U.S. revenue for the overall agency business increased 6.5% to a record $46.8 billion in 2015.

Digital's share of U.S. marketing spending continues to grow. Digital captured 41.3% of U.S. agency revenue in 2015 ($19.3 billion out of $46.8 billion; numbers rounded), up from 39.7% in 2014 and 25.8% in 2009, according to Ad Age.

U.S. revenue rose last year in all major agency disciplines, with gains from 3.8% for customer relationship management/direct marketing to 8.7% for healthcare marketing. Ad agency revenue increased 4.8% in 2015. Public relations and promotion disciplines grew 5.0% and 5.1%, respectively.

"The agency business is adapting to demands from marketers to make digital the center of marketing," said Bradley Johnson, Ad Age's director of data analytics. "But the old-line consolidators of Madison Avenue -- WPP, Omnicom Group, Publicis Groupe, Interpublic Group of Cos. -- face growing competition from deep-pocketed consulting and tech players that are making inroads with marketers."

Among the world's five biggest digital agency networks ranked by Ad Age, only one is part of an established agency company: No. 5 Wunderman, owned by WPP.

Ad Age ranks Accenture plc's Accenture Interactive as the world's biggest digital agency network, followed by IBM Corp.'s IBM Interactive Experience, Deloitte Touche Tohmatsu's Deloitte Digital and Alliance Data Systems Corp.'s Epsilon.

Agency Report 2016 tracks revenue and growth rates for more than 1,000 agencies, agency networks and agency companies.