Simon Property Group is the largest retail U.S. REIT, operating distinct platforms for regional malls, premium outlet centers, and international properties, among others. At year-end 2012, Simon owned or had an interest in more than 300 properties comprising nearly 250 million square feet of gross leasable space in North America and Asia. In March 2012, it acquired a 29% interest in Klepierre, which owns shopping centers in 13 countries in Europe. U.S. Regional malls and premium outlet centers contribute about 80% of net operating income.