X0306 4 2017-12-15 0 0000866609 ION GEOPHYSICAL CORP IO 0001507574 Williamson Ken 2105 CITYWEST BOULEVARD SUITE 100 HOUSTON TX 77042-2855 0 1 0 0 EVP&COO, E&P TECHNO & SERVICES Common Stock 2017-12-15 4 P 0 26000 13.6267 A 73949 D Common Stock 2017-12-15 4 M 0 100000 3.10 A 173949 D Common Stock 2017-12-15 4 D 0 100000 13.05 D 73949 D Stock Appreciation Right 3.10 2017-12-15 4 M 0 100000 0.00 D 2017-03-01 2026-03-01 Common Stock 100000 50000 D This transaction was executed in multiple trades at prices ranging from $13.5824 to $13.70, inclusive. The price set forth above reflects the weighted-average price per share. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transactions were effected. Exercise of cash-settled SARs. In accordance with the rules for filing Form 4, the exercise of cash-settled SARs is treated as the simultaneous purchase of the number of shares for which SARs are exercised and the sale of the same number of shares. No shares actually changed hands. Compensation Committee approved acceleration of the vesting of the second tranche on 12/13/2017. Final tranche to vest as scheduled on 03/01/2019. Rebecca F. Sacco, attorney-in-fact 2017-12-19