Windows Division revenue increased $839 million. Surface revenue was $853 million. Revenue from commercial licensing of Windows increased $487 million, while unearned revenue from commercial licensing also increased, reflecting continued support of our platform. In addition, we recognized $540 million of previously deferred revenue related to the expiration of the Windows Upgrade Offer. Partially offsetting these increases was a decrease in OEM revenue.
OEM revenue decreased 3%. Excluding the impact of the Windows Upgrade Offer, OEM revenue decreased 10%. This decrease primarily reflects the impact on revenue of the decline in the x86 PC market, which we estimate declined approximately 9%.
In May 2013, we announced that we had surpassed 100 million licenses sold for Windows 8.
Windows Division operating income decreased, primarily due to higher cost of revenue and sales and marketing expenses, offset in part by revenue growth. Cost of revenue increased $1.8 billion, reflecting a $1.6 billion increase in product costs associated with Surface and Windows 8, including a charge for Surface RT inventory adjustments of approximately $900 million. Sales and marketing expenses increased $1.0 billion or 34%, reflecting an $898 million increase in advertising costs associated primarily with Windows 8 and Surface.