Earnings per Share

The Company has unvested restricted stock units outstanding that are considered participating securities and, therefore, computes basic and diluted earnings per share under the two-class method. Basic earnings per share for the periods are based upon the weighted average number of shares of common stock outstanding during the periods. Diluted earnings per share include the effect of certain stock options.



	Year Ended December 31,
	2017			2016			2015
Net income attributable to Westlake Chemical Corporation	$	1,304		$	399		$	646
Less:
Net income attributable to participating securities	(7		)	(2		)	(3		)
Net income attributable to common shareholders	$	1,297		$	397		$	643

The following table reconciles the denominator for the basic and diluted earnings per share computations shown in the consolidated statements of operations:



	Year Ended December 31,
	2017		2016		2015
Weighted average common shares—basic	129,087,043		129,367,712		131,823,707
Plus incremental shares from:
Assumed exercise of options	452,970		607,110		478,105
Weighted average common shares—diluted	129,540,013		129,974,822		132,301,812

Earnings per common share attributable to Westlake Chemical Corporation:
Basic	$	10.05	$	3.07	$	4.88
Diluted	$	10.00	$	3.06	$	4.86

There are no antidilutive options to purchase shares of common stock for the year ended December 31, 2017. Excluded from the computation of diluted earnings per share for the years ended December 31, 2016 and 2015 are options to purchase 318,259 and 301,969 shares of common stock, respectively. These options were outstanding during the periods reported but were excluded because the effect of including them would have been antidilutive.