Basic earnings per share is computed using the weighted average number of common shares outstanding during the period, and diluted earnings per share is computed using the weighted average number of common shares outstanding during the period adjusted for all potentially dilutive common stock equivalents, except in cases where the effect of the common stock equivalent would be antidilutive. The amounts used to compute the basic and diluted earnings per share for the three and six months ended June 30, 2013 and 2012 are illustrated below (in thousands):

For purposes of calculating diluted earnings per share, there were no adjustments required to derive Quanta’s net income attributable to common stock. For the three and six months ended June 30, 2013 and 2012, a nominal number of stock options were excluded from the computation of diluted earnings per share because the exercise prices of the stock options were greater than the average market price of Quanta’s common stock. The outstanding exchangeable shares of a Canadian subsidiary of Quanta that were issued pursuant to the acquisition of Valard Construction LP and certain of its affiliated entities (Valard) on October 25, 2010, which are exchangeable on a one-for-one basis with shares of Quanta common stock, are included in weighted average shares outstanding for basic and diluted earnings per share for the three and six months ended June 30, 2013 and 2012.