As filed with the Securities and Exchange Commission on February 15, 2018

Registration No. 333-

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

Form S-3

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

ION GEOPHYSICAL CORPORATION (Exact name of registrant as specified in its charter)

Delaware 22-2286646 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification No.)

2105 CityWest Blvd., Suite 100 Houston, Texas 77042 (281) 933-3339 (Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Matt Powers Executive Vice President, General Counsel and Secretary ION Geophysical Corporation 2105 CityWest Blvd., Suite 100 Houston, Texas 77042 (281) 933-3339 (Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

J. Eric Johnson Locke Lord LLP 600 Travis Street, Suite 2800 Houston, Texas 77002 Telephone: (713) 226-1200 Telecopy: (713) 229-2642

Approximate date of commencement of proposed sale to the public: From time to time after this registration statement becomes effective.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. o

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box. x

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. x 333-213769

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. o

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer o Accelerated filer x Non-accelerated filer o Smaller reporting company o (Do not check if a Emerging growth company o

smaller reporting company)

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

CALCULATION OF REGISTRATION FEE

Proposed Maximum Amount of Title of Each Class of Securities Aggregate Offering Registration

to Be Registered Price(1) Fee(2) Common Stock, par value $.01 per share

Warrants

Total $ 20,000,000 $ 2,490

(1) The Registrant previously registered common stock, preferred stock, debt securities, warrants, units and other securities with an aggregate offering price of $100,000,000 on a Registration Statement on Form S-3 (File No. 333-213769), as amended, which was declared effective December 2, 2016. In accordance with Rule 462(b) promulgated under the Securities Act of 1933, an additional amount of common stock having a proposed maximum aggregate offering price of $20,000,000 is hereby registered representing no more than 20% of the maximum aggregate offering price of securities available for issuance under the Registration Statement on Form S-3 (File No. 333- 213769). In no event will the maximum aggregate offering price of all securities issued pursuant to this Registration Statement and the Registration Statement on Form S-3 (File No. 333-213769) exceed those registered under such registration statements. (2) Calculated in accordance with Rule 457(o). Represents the registration fee only for the additional amount of securities being represented hereby. The Registrant previously registered securities pursuant to a Registration Statement on Form S-3 (File No. 333-213769), as amended, for which a fee of $10,070 was paid.

This Registration Statement shall become effective upon filing with the Commission in accordance with Rule 462(b) under the Securities Act of 1933, as amended.

EXPLANATORY NOTE AND INCORPORATION BY REFERENCE

We are filing this Registration Statement on Form S-3 with the U.S. Securities and Exchange Commission pursuant to Rule 462(b) and General Instruction IV of Form S-3, both as promulgated under the Securities Act of 1933, as amended. This Registration Statement on Form S-3 relates to the public offering of securities contemplated by the Registration Statement on Form S-3 (File No. 333-213769), filed with the Securities and Exchange Commission on September 23, 2016, as amended, which was previously declared effective by the Commission on December 2, 2016. This Registration Statement on Form S- 3 is being filed for the sole purpose of increasing the maximum aggregate offering price of the securities registered for sale by the Registrant. We are registering an additional amount of securities equal to 20% of the remaining $100,000,000 of securities eligible to be sold under Registration Statements No. 333-213769, or $20,000,000 of additional securities, for a total maximum in the aggregate of $120,000,000. The contents of the Registration Statement No. 333-213769 is hereby incorporated by reference into this Registration Statement in its entirety, including each of the documents we filed with the Securities and Exchange Commission and incorporated or deemed to be incorporated by reference therein and all exhibits thereto.

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PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 16. Exhibits.

Exhibit No. Description of Exhibit 5.1* Opinion of Locke Lord LLP with respect to legality of the securities, including consent.

23.1* Consent of Grant Thornton LLP.

23.3* Consent of Locke Lord LLP (included in Exhibit 5.1).

24.1 Power of Attorney (filed as Exhibit 24.1 to the Registration Statement on Form S-3 filed by the Registrant on September 23, 2016, File No. 333-213769), incorporated herein by reference.

* Filed herewith.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the city of Houston, State of Texas, on the 15th day of February, 2018.

ION GEOPHYSICAL CORPORATION

By: /s/ MATT POWERS

Matt Powers

Executive Vice President,

General Counsel and

Corporate Secretary

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed by the following persons in the capacities and on the dates indicated.

Signature Title Date

/s/ R. BRIAN HANSON Chief Executive Officer President and Director February 15, 2018

R. Brian Hanson (Principal Executive Officer)

/s/ STEVEN A. BATE Executive Vice president and Chief Financial Officer February 15, 2018

Steven A. Bate (Principal Financial Officer)

/s/ SCOTT SCHWAUSCH Vice President and Corporate Controller (Principal February 15, 2018

Scott Schwausch Accounting Officer)

/s/ * Chairman of the Board February 15, 2018

James M. Lapeyre, Jr.

/s/ * Director February 15, 2018

David H. Barr

/s/ * Director February 15, 2018

Hao Huimin

/s/ * Director February 15, 2018

Michael C. Jennings

/s/ * Director February 15, 2018

Franklin Myers

/s/ * Director February 15, 2018

S. James Nelson, Jr.

/s/ * Director February 15, 2018

John N. Seitz

* By /s/ R. BRIAN HANSON

R. Brian Hanson

(Attorney-in-fact for each person indicated)

4 Exhibit 5.1

2800 JPMorgan , 600 Travis Houston, TX 77002 Telephone: 713-226-1200 Fax: 713-223-3717 www.lockelord.com

February 15, 2018

ION Geophysical Corporation 2105 CityWest Blvd., Suite 100 Houston, Texas 77042

Ladies and Gentlemen:

We have acted as counsel for Ion Geophysical Corporation, a Delaware corporation (the “Company”), in connection with the Company’s filing of a registration statement registration on Form S-3 (the “Registration Statement”) pursuant to Rule 462(b) the Securities Act of 1933, as amended (the “Securities Act”), relating to an aggregate of $20,000,000 of: (i) shares of common stock, par value $.01 per share, of the Company (“Common Stock”) and (ii) warrants to purchase Common Stock (the “Warrants,” and together with the Common Stock, each a “Security” and collectively the “Securities”), all as more fully described in the Registration Statement.

We have examined those records and documents as we have deemed necessary, including but not limited to originals, photocopies or conformed copies of: (i) the Registration Statement (including the exhibits thereto); (ii) the Restated Certificate of Incorporation and Bylaws of the Company, each as amended to date; (iii) the corporate proceedings of the Company; and (iv) all other certificates, agreements and documents that we have considered relevant and necessary as a basis for the opinions expressed in this letter. In addition, we have made those other examinations of law and fact as we considered necessary to form a basis for our opinions.

As to certain questions of fact material to our opinions that we have not independently established, we have relied upon representations of public officials and upon certificates from officers of the Company.

In rendering the following opinions, we have assumed: (i) all information contained in all documents reviewed by us is true and correct; (ii) the genuineness of all signatures on all documents reviewed by us; (iii) the authenticity and completeness of all documents submitted to us as originals; (iv) the conformity to authentic originals of all documents submitted to us as certified or photostatic copies; and (v) each natural person signing any document reviewed by us had the legal capacity to do so. We have also assumed the due authorization, execution and delivery of all documents where authorization, execution and delivery are prerequisites to the effectiveness of such documents.

Based on the foregoing, and subject to the assumptions, exceptions and qualifications stated herein, we are of the opinion that the Securities, up to an aggregate offering price of $20,000,000 when issued against payment therefor, will be validly issued, fully paid and non-assessable.

The opinions expressed in this letter are limited to the laws of the State of Texas, the General Corporation Law of the State of Delaware and the federal securities laws of the United States of America.

Please note that we are opining only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters.

We consent to the use of this opinion as Exhibit 5.1 to the Registration Statement and to the reference to our firm under the caption “Legal Matters” in the prospectus included as a part of the Registration Statement. In giving this consent, we do not admit that this firm is in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Securities and Exchange Commission promulgated thereunder.

This opinion is rendered on the date hereof and we disclaim any duty to advise you regarding any changes in the matters addressed herein.

Very truly yours,

/s/ Locke Lord LLP

LOCKE LORD LLP

Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We have issued our reports dated February 8, 2018 with respect to the consolidated financial statements, schedule, and internal control over financial reporting of ION Geophysical Corporation incorporated by reference from the Annual Report on Form 10-K for the year ended December 31, 2017 in the Registration Statement on Form S-3, as amended (File No. 333-213769), which are incorporated by reference in this Registration Statement on Form S- 3MEF. We consent to the incorporation by reference of the aforementioned reports in this Registration Statement.

/s/ Grant Thornton LLP

Houston, Texas February 15, 2018