Google will earn more US display advertising revenues than any other company this year, topping the market with a 15.4% share, according to estimates by market research firm eMarketer.

The milestone means Google now holds more share than any other company in each of the US search, display and mobile advertising markets.

eMarketerexpects Google to take home $2.31 billion in US display ad revenues this year, up 38.5% from $1.67 billion in 2011. Facebook will earn $2.16 billion in US display ad revenues this year, up 24.4% from $1.73 billion last year. Yahoo! - the longtime leader before Facebook topped it last year - will see its share fall further.

This year, the overall US display ad market will grow 21.5% to $14.98 billion from $12.33 billion in 2011, eMarketer estimates, driven by the expansion of both Google and Facebook as advertising platforms; the continued health of banner spending due to the expansion of inventory, aided by mobile growth; and increased spending on digital video advertising, especially YouTube.

Combined, Google and Facebook will represent just below 30% of total display ad revenues by the end of 2012. Yahoo will account for 9.3% of total display ad revenues this year, while Microsoft and AOL will each make up less than 5% of the total, eMarketer estimates. These three companies will decrease in share as Google and Facebook expand.