Earnings per Share

3 Months Ended

Mar. 31, 2021

10. EARNINGS PER SHARE

We compute basic earnings per common share by dividing net income attributable to Core Laboratories N.V. by the weighted average number of common shares outstanding during the period. Diluted earnings per common and potential common shares include additional shares in the weighted average share calculations associated with the incremental effect of dilutive restricted stock awards and contingently issuable shares, as determined using the treasury stock method. The following table summarizes the calculation of weighted average common shares outstanding used in the computation of diluted earnings per share (in thousands):

	Three Months Ended
	March 31,
	2021		2020
Weighted average basic common shares outstanding		45,177		44,447
Effect of dilutive securities:
Performance shares		516		—
Restricted stock		271		—
Weighted average diluted common and potential common shares outstanding		45,964		44,447

For the three months ended March 31, 2020, the number of outstanding performance and restricted shares of Core Laboratories N.V. common stock that were excluded from the diluted earnings per share calculation, as their impact would be antidilutive, were as follows (in thousands):

	Three Months Ended
	March 31, 2020
Performance shares		398
Restricted stock		9