eMarketer estimates marketers will continue to invest in search engine marketing with ad spend initially this year boosted somewhat by major national elections and the Summer Olympic Games. Search spending will rise 27% to $19.51 billion. By 2016, search ad spending in the U.S. will approach $30 billion. Google, Microsoft, Yahoo and AOL by 2014 will account for 92.1% of all U.S. search ad revenue, and 44.3% of all U.S. online ad revenue, according to eMarketer. That's up from just under 90% of all search ad revenue and 43% of all U.S. online ad revenues in 2011, the research firm explains.