Peter Fleischer said the company "could do better" with policy statements that explained why user information was sometimes shared with third parties.
Mr Fleischer said Google would never give "identifiable personal data" to third parties, including advertisers.
A working party of European Information Commissioners has written to Google to ask the firm to explain why it holds on to users' web history data for up to two years.
Google has said it would respond by the end of June.
There is also growing concern from privacy campaigners over the implication of Google's proposed purchase of advertising firm DoubleClick.
The ad company helps link up advertising agencies, marketers and web site publishers hoping to put adverts online.
View: BBC News