GOOGLE Inc raised its offer for Motorola Mobility Holdings Inc by 33 percent to US$12.5 billion over two weeks of negotiations between the two companies, a regulatory filing has showed.

Google originally offered US$30 for every Motorola share on August 1 - but eventually paid US$40 - as the Internet powerhouse sought Motorola's massive patent portfolio, after losing out on the Nortel patent auction to a consortium, including Apple and Microsoft.

On August 5, Frank Quattrone's Qatalyst Partners, who advised Motorola on the deal, suggested the company reject the initial bid and seek an offer of US$43.50 a share instead, according to a filing by Motorola with the United States Securities and Exchange Commission on Tuesday.

On August 9, Google came back with an offer of US$37 per share, but Sanjay Jha, Motorola's CEO, said he would be prepared to recommend that the company consider accepting an offer of US$40.50 a share or higher.

On the same day, Google raised its price to US$40 per share.