Google was willing to pay 33 percent more – to $12.5 billion – for Motorola Mobility Holdings after offers and counter-offers during what appears to be some intense negotiations, according to news reports.

The two companies spent two weeks negotiating the deal, according to Reuters, citing information from a new filing from the U.S. Securities and Exchange Commission. Early in the process, Google was willing to pay $30 per Motorola share but then paid $40 a share. The $40 per Motorola share, announced on August 15, was a 63 percent premium to the company’s close on August 12.

The boards of both companies have approved the deal, according to TechZone360.

TechZone360 also reported that Motorola Mobility was in talks with several other interested parties, including Microsoft.  The talks were going on for a lengthy period of time.

The main draw for Google with Motorola appears to be its numerous patents. “The deal it struck gives it access to Motorola Mobility’s strong portfolio of 17,000 current patents and 7,500 patent applications across wireless standards and non-essential patents on wireless service delivery,” Gigaom said.

Microsoft was also interested in Motorola Mobility’s numerous patents. The patents, in Microsoft’s hands, could have hurt Google’s Android operating system, Forbes said.

The Google-Motorola Mobility deal is subject to closing conditions, such as regulatory approvals in the United States, the European Union and other locations, and the approval of Motorola Mobility’s stockholders. The transaction is expected to close by the end of 2011 or early 2012, according to media reports.

“Motorola Mobility’s total commitment to Android has created a natural fit for our two companies,” Larry Page, CEO of Google, said in a company statement when the deal was announced. “Together, we will create amazing user experiences that supercharge the entire Android ecosystem for the benefit of consumers, partners and developers.”