X0306 4 2021-03-23 0 0001666134 BLACKLINE, INC. BL 0001688365 Tucker Therese 21300 VICTORY BLVD., 12TH FLOOR WOODLAND HILLS CA 91367 1 1 0 0 Executive Chair Common Stock 2021-03-23 4 S 0 2200 111.2909 D 120179 D Common Stock 2021-03-23 4 S 0 5355 112.5194 D 114824 D Common Stock 2021-03-23 4 S 0 2445 113.0133 D 112379 D Common Stock 2298482 I Brian & Therese Tucker Living Trust Common Stock 874128 I Tucker Legacy Trust Common Stock 577200 I Isaac Tucker 2012 Irrevocable Trust Common Stock 577200 I Roseanna Tucker 2012 Irrevocable Trust Common Stock 250916 I Tucker Seimetz Safety Net Trust Common Stock 54074 I Claire Seimetz 2015 Trust The sale transaction reported on this Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on November 27, 2020. The sale price represents the weighted-average price of shares sold ranging from $110.89 to $111.885 per share. Upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4. The sale price represents the weighted-average price of shares sold ranging from $112.015 to $112.875 per share. Upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4. The sale price represents the weighted-average price of shares sold ranging from $112.90 to $113.42 per share. Upon request by the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4. /s/ Karole Morgan-Prager, Attorney-in-Fact 2021-03-24