X0306 4 2021-03-12 0 0001666134 BLACKLINE, INC. BL 0001603951 Huffman Marc 21300 VICTORY BLVD., 12TH FLOOR WOODLAND HILLS CA 91367 1 1 0 0 Chief Executive Officer Common Stock 2021-03-12 4 S 0 3285 110.512 D 152132 D Common Stock 2021-03-12 4 S 0 8419 111.544 D 143713 D Common Stock 2021-03-12 4 S 0 6750 112.516 D 136963 D Common Stock 2021-03-12 4 S 0 3837 113.232 D 133126 D The sale transaction reported on this Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on December 4, 2020. The sale price represents the weighted-average price of shares sold ranging from $110.00 to $110.94 per share. Upon request by the 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 $111.00 to $111.97 per share. Upon request by the 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 $112.02 to $112.99 per share. Upon request by the 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 $113.00 to $113.64 per share. Upon request by the 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 2021-03-15