partially offset by a decrease in net sales of iPad and Mac. 

The growth in net sales during 2012 was mainly due to strong demand for the third generation iPad. The Rest of Asia Pacific segment experienced significantly lower year-over-year growth in net sales compared to all of the Company’s other operating segments due primarily to a decrease in iPhone sales. This decrease reflects the timing of iPhone 5 launches in the Rest of Asia Pacific segment, which only occurred in a limited number of countries during the fourth quarter of 2012. 

The growth in net sales during 2013 was primarily driven by increased unit sales of iPhone and iPad following the new product introductions in the first half of 2013 and increased sales of services. With an average of 403 and 365 open stores during 2013 and 2012, respectively, average revenue per store decreased to $50.2 million in 2013, compared to $51.5 million in 2012. 

The growth in net sales during 2012 was driven primarily by increased demand for iPhone following the launches of iPhone 4s and iPhone 5, strong demand for the third generation iPad and iPad 2, and higher Mac net sales. Lower year-over-year growth in net sales in the Retail segment during 2012 compared to the Company’s other segments reflects the significant growth in iPad indirect distribution channel expansion. With an average of 365 stores and 326 stores during 2012 and 2011, respectively, average revenue per store increased 19% to $51.5 million in 2012 compared to $43.3 million in 2011. 

The Retail segment’s operating income was $4.0 billion, $4.6 billion and $3.1 billion during 2013, 2012, and 2011, respectively. The year-over- year decrease in Retail operating income in 2013 is primarily attributable to lower gross margin similar to that experienced by the Company overall, partially offset by higher net sales. The year-over-year increase in Retail operating income in 2012 is primarily attributable to higher overall net sales that resulted in significantly higher average revenue per store during 2012. 

The gross margin percentage in 2013 was 37.6% compared to 43.9% in 2012. The year-over-year decrease in gross margin in 2013 compared to 2012 was driven by multiple factors including introduction of new versions of existing products with higher cost structures and flat or reduced pricing; a shift in sales mix to products with lower margins; introduction of iPad mini with gross margin significantly below the Company’s average product margins; higher expenses associated with changes to certain of the Company’s service policies and other warranty costs; price reductions on certain products, including iPad 2 and iPhone 4; and unfavorable impact from foreign exchange fluctuations. 

The gross margin percentage in 2012 was 43.9%, compared to 40.5% in 2011. This year-over-year increase in gross margin was largely driven by lower commodity and other product costs, a higher mix of iPhone sales, and improved leverage on fixed costs from higher net sales. The increase in gross margin was partially offset by the impact of a stronger U.S. dollar. The gross margin percentage during the first half of 2012 was 45.9% compared to 41.4% during the