The European Commission has up to now only confirmed four cases against Google. The addition of fresh complaints could broaden the EU watchdog's ongoing probe and pile pressure on the company to strike a settlement.
"The Commission has nine formal complaints now. The new complaints come from small companies," said one of the sources who declined to provide details because of the sensitivity of the matter.
The second source said three cases came from national regulators while two were fresh complaints.
The Commission opened an investigation into Google in November last year following allegations by three small companies that Google demoted their sites in Web search engines because they were rivals.
Microsoft ratcheted up its rivalry with Google by filing its first-ever complaint to the EU watchdog in March this year, claiming that Google systematically blocked Internet search competition.
The Commission can fine companies up to 10 percent of their global turnover for breaching EU rules. It has in recent years imposed billion-euro penalties on Microsoft and Intel for anticompetitive behaviour.
The US Federal Trade Commission is also investigating Google following accusations that it abused its market dominance. The U.S. Senate's antitrust panel will hold a hearing on Google's market clout on Sept. 21.
EurActiv with Reuters