 While the RFS requirement is increasing by about 23%—from in 2008 to in 2009—the percentage requirement is increasing by nearly one third, from 7.76% in 2008 to 10.21% in 2009.The EPA determines that fuel blenders are meeting renewable fuel requirements by examining Renewable Identification Numbers that they submit to the agency.The 2009 RFS is also pushing up against what is known as the "blend wall".