C3is Inc (CISS) majority holder updates 68.8% stake

Rhea-AI Filing Summary

Imperial Petroleum Inc., a Marshall Islands corporation, has filed Amendment No. 12 to its beneficial ownership report on the common stock of C3is Inc. Imperial Petroleum reports beneficial ownership of 28,846,153 shares of common stock, representing 68.8% of the outstanding class, with sole voting and dispositive power over these shares.

The amendment reflects an adjustment of the conversion price of C3is’s 5.0% Series A Cumulative Convertible Perpetual Preferred Stock to $0.52, triggered by C3is’s sale of common stock in a registered offering described in a prospectus dated July 28, 2026, and an updated total share count. Imperial Petroleum acquired its position in connection with a spin-off distribution and intends to review its investment on an ongoing basis, with flexibility to buy, hold, or sell shares and to consider a wide range of potential corporate actions. Harry N. Vafias, Imperial Petroleum’s Chairman, Chief Executive Officer and President, serves as Non-Executive Chairman of C3is and beneficially owns 753 C3is shares, while two other shared directors hold no C3is shares.

Key Figures

Beneficially owned shares: 28,846,153 shares Ownership percentage: 68.8% Conversion price: $0.52 +3 more

6 metrics

Beneficially owned shares 28,846,153 shares Common stock beneficially owned by Imperial Petroleum with sole voting and dispositive power

Ownership percentage 68.8% Percent of C3is common stock class represented by Imperial Petroleum’s beneficial ownership

Conversion price $0.52 Adjusted conversion price of 5.0% Series A Cumulative Convertible Perpetual Preferred Stock

Series A dividend rate 5.0% Stated rate on Series A Cumulative Convertible Perpetual Preferred Stock of C3is

Vafias shareholdings 753 shares C3is common shares beneficially owned by Harry N. Vafias through entities as of the date

Event date 07/28/2026 Date of the event requiring the ownership update and related prospectus filing reference

Key Terms

beneficially owned, Sole Voting Power, Sole Dispositive Power, Series A Cumulative Convertible Perpetual Preferred Stock, +2 more

6 terms

beneficially owned financial

"updates the number of shares of Common Stock beneficially owned by Imperial Petroleum"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

Sole Voting Power financial

"Number of Shares Beneficially Owned by Each Reporting Person With: Sole Voting Power 28,846,153.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

Sole Dispositive Power financial

"Number of Shares Beneficially Owned by Each Reporting Person With: Sole Dispositive Power 28,846,153.00"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

Series A Cumulative Convertible Perpetual Preferred Stock financial

"conversion price of the 5.0% Series A Cumulative Convertible Perpetual Preferred Stock"

Spin-Off Distribution financial

"The Reporting Person involved in the securities described in this in connection with the Spin-Off Distribution"

Schedule 13D regulatory

"events listed in Item 4(a) through 4(j) of Schedue 13D"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 07/30/2026 - 07:00 PM Accepted by SEC EDGAR 07/30/2026 - 07:00 PM Learn about SEC filing dates

FAQ

What ownership stake in C3is Inc (CISS) does Imperial Petroleum report?

Imperial Petroleum reports beneficial ownership of 28,846,153 C3is common shares, representing 68.8% of the outstanding class. The company holds sole voting and sole dispositive power over these shares, indicating it can vote and decide on dispositions without shared control.

Why did Imperial Petroleum amend its C3is Inc (CISS) Schedule 13D in Amendment No. 12?

Amendment No. 12 updates the number and percentage of C3is shares Imperial Petroleum beneficially owns. The changes stem from a revised $0.52 conversion price for Series A Convertible Preferred Stock and the new number of outstanding common shares after a registered offering.

What is the new conversion price for C3is Inc (CISS) Series A Convertible Preferred Stock?

The conversion price of C3is’s 5.0% Series A Cumulative Convertible Perpetual Preferred Stock has been adjusted to $0.52 per share. This change occurred under the security’s terms following C3is’s registered sale of common stock described in a prospectus filed on July 28, 2026.

How does Imperial Petroleum describe its future intentions toward C3is Inc (CISS)?

Imperial Petroleum states it will review its investment on a continuing basis and may buy additional C3is securities, hold, or sell shares. It may also consider discussions and potential extraordinary corporate transactions, depending on business performance, market conditions, liquidity, tax factors and other considerations.

What board and management overlap exists between Imperial Petroleum and C3is Inc (CISS)?

Harry N. Vafias, Chairman, CEO and President of Imperial Petroleum, serves as C3is’s Non-Executive Chairman and owns 753 C3is shares through entities. Directors John Kostoyannis and George Xiradakis sit on both boards and currently own no C3is common shares.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 12)

C3is Inc.

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

Y18284300

(CUSIP Number)

Harry N. Vafias
331 Kifissias Avenue, Kifissia,
Athens, J3, 14561
011 30210 625 0001

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

07/28/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): Y18284300

1

Name of reporting person

Imperial Petroleum Inc.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

MARSHALL ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 28,846,153.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 28,846,153.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

28,846,153.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

68.8 %

14

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.01 per share
(b)	Name of Issuer: C3is Inc.
(c)	Address of Issuer's Principal Executive Offices: 331 Kifissias Avenue, Kifissia, Athens, GREECE , 14561.
Item 1 Comment: This Amendment No. 12 (this "Amendment No. 12") to Schedule 13D (originally filed on July 28, 2023 and amended by Amendment No. 1 filed on January 24, 2024, Amendment No. 2 filed on March 20, 2024, Amendment No. 3 filed on May 1, 2024, Amendment No. 4 on January 14, 2025, Amendment No. 5 filed on April 15, 2025, Amendment No. 6 filed on October 10, 2025, Amendment No. 7 filed on December 15, 2025, Amendment No. 8 filed on December 30, 2025, Amendment No. 9 filed on February 4, 2026, Amendment No. 10 filed on May 6, 2026 and Amendment No. 11 filed on June 24, 2026), relates to the common stock, par value $0.01 per share ("Common Stock"), of C3is Inc., a Marshall Islands corporation (the "Issuer"), and is being filed by Imperial Petroleum Inc., a Marshall Islands corporation ("Imperial Petroleum" or the "Reporting Person"). Information given in response to each item below shall be deemed incorporated by reference in all other items below. Unless indicated otherwise, all items left blank remain unchanged, and any items which are amended below are deemed to amend and update the existing items in the Schedule 13D.
Item 3.	Source and Amount of Funds or Other Consideration
	Item 3 of the statement is hereby amended by adding the following paragraphs to the end of Item 3: This Amendment No. 12 updates the number of shares of Common Stock beneficially owned by Imperial Petroleum as a result of changes in the conversion price of the 5.0% Series A Cumulative Convertible Perpetual Preferred Stock, par value $0.01 per share (the "Series A Convertible Preferred Stock"), of the Issuer. The conversion price has been adjusted to $0.52 pursuant to the terms of the Series A Convertible Preferred Stock as a result of as a result of the Issuer's sale of its Common Stock in a registered offering, as reported in the Issuer's prospectus filed with the Securities and Exchange Commission (the "SEC") on July 28, 2026. This Amendment No. 12 is also being filed to update the percentage of shares of Common Stock of the Issuer beneficially owned by Imperial Petroleum to reflect dilution in percentage ownership based on the revised total number of outstanding shares of Common Stock following the offering. Harry N. Vafias, the Chairman, Chief Executive Officer and President of Imperial Petroleum, is the Non-Executive Chairman of the Issuer and is the beneficial owner of 753 shares of Common Stock, including through Arethusa Properties LTD and Flawless Management, Inc., as of the date hereof. John Kostoyannis and George Xiradakis, each a director of Imperial Petroleum, are each a director of the Issuer and own nil and nil shares of Common Stock, respectively, as of the date hereof.
Item 4.	Purpose of Transaction
	The Reporting Person involved in the securities described in this Schedule 13D in connection with the Spin-Off Distribution, and intends to review its investment in the Issuer on a continuing basis. The Reporting Person may from time to time acquire additional securities of the Issuer, or retain or sell all or portion of the shares then held by the Reporting Person, in the open market, block trades, underwritten public offerings or privately negotiated transactions. Any actions the Reporting Person might undertake with respect to its investment in the Issuer may be made at any time and from time to time and will be dependent upon the Reporting Person's review of numerous factors, including, but not limited to: ongoing evaluation of the Issuer's business, financial condition, operations, prospects and strategic alternatives; price levels of the Issuer's securities; general market, industry and economic conditions; the relative attractiveness of alternative business and investment opportunities; tax considerations; liquidity of the Issuer's securities; and other factors and future developments. Mr. Vafias serves as the Non-Executive Chairman of the Issuer and John Kostoyannis and George Xiradakis each serve as a director of the Issuer, other shareholders of the Issuer and other relevant parties, which discussions may include matters ranging from the operations and conduct of the Issuer's business to considering or exploring extraordinary corporate transactions including the events listed in Item 4(a) through 4(j) of Schedue 13D. In connection with these discussions, the Reporting Person may, either directly or through one or more affiliates, determine to take any available course of action or to take no course of action and may at any time and from time to time take steps to further or implement such course of action, including any of the events listed in Item 4(a) through 4(j) of Schedule 13D. Any action or actions the Reporting Person may undertake with respect to its investment in the Issuer or the operations and conduct of the Issuer's business will be dependent upon the Reporting Person's review of numerous factors, including those listed above, and the Reporting Person specifically reserves the right to change its intentions, or to formulate plans and proposals, with respect to any or all of the matters described in this paragraph, subject to applicable law and regulations.
Item 5.	Interest in Securities of the Issuer
(a)	The responses of Imperial Petroleum to Rows (7) through (11) of the cover page of this Schedule are incorporated herein by reference. Except as set forth herein, neither Imperial Petroleum nor, to the knowledge of Imperial Petroleum, the Covered Persons beneficially own any Common Stock as of the date of this filing.
(b)	The responses of Imperial Petroleum to Rows (7) through (11) of the cover page of this Schedule are incorporated herein by reference. Except as set forth herein, neither Imperial Petroleum nor, to the knowledge of Imperial Petroleum, the Covered Persons beneficially own any Common Stock as of the date of this filing.
(c)	The information set forth in Item 3 is hereby incorporated herein by reference. Other than as set forth in this Schedule, neither Imperial Petroleum nor, to the best of its knowledge, any of the Covered Persons has engaged in any transaction in any Common Stock during the past 60 days.
(d)	No other person is known to Imperial Petroleum to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the shares of the Common Stock covered by this Schedule.
(e)	Not applicable.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Imperial Petroleum Inc.

Signature:	/s/ Harry N. Vafias
Name/Title:	Chief Executive Officer
Date:	07/30/2026