A report by accounting firm PricewaterhouseCoopers found that the average effective three-year corporate tax rate for U.S. based corporations rose to 26.3 percent, up 0.7 percent from the previous year. The effective tax rate is the tax rate after expenses and tax offsets.
http://www3.cfo.com/article/2012/5/tax_tax-incentives-effective-tax-rate-