The Australian Competition and Consumer Commission said on its Web site it has launched an informal review of, writing to industry participants for comments on how the takeover would affect the Australian market.
It is seeking comment on the extent to which the two companies compete in the local online advertising market, whether a merged company would lead to higher prices, and whether it would have the ability to send rival search engines or advertisers out of business.
The ACCC said it expected to announce a decision on October 16.
DoubleClick, a U.S. Web advertising supplier, connects ad agencies, marketers and Web site publishers, and has more than 1,500 corporate clients.
A Google spokesman said online advertising in Australia was highly competitive, and had a large number of participants and new entrants.
"DoubleClick and Google provide very different services to each other and we've provided information to the ACCC in the normal course," spokesman Rob Shilkin told Reuters.
The DoubleClick deal has
Rivals including Microsoft and AT&T have asked U.S. antitrust officials to look closely at the proposed takeover, saying Google could gain too much control over online advertising.
The Australian competition watchdog has taken Google to court in a separate case, alleging that sponsored advertising links on Google's Web site in 2005.
The ACCC said Google had not done enough to distinguish between sponsored advertising links and the search links that result when customers type keywords into Google's Web search system, which it asserted was deceptive.
At a Federal Court hearing in Sydney on Monday, lawyers for the ACCC argued that Google allowed sponsored links to appear in the same format as actual search results.
Lawyers for Google successfully argued for orders that the ACCC file a two-page summary of its case, and the judge described the ACCC claim as "opaque and repetitious," the Australian Associated Press reported from the court.
The case was adjourned for a directions hearing on October 4.
Google has said it would vigorously fight the allegations.