Imperial Petroleum controls 80.5% of C3is

Rhea-AI Filing Summary

C3is Inc. (symbol CISS) has an updated ownership report showing that Imperial Petroleum Inc. beneficially owns 6,136,475 shares of C3is common stock, representing 80.5% of the outstanding common shares, with sole voting and dispositive power over all of these shares.

This amendment reflects changes arising from an adjustment of the conversion price of C3is’s 5.0% Series A Cumulative Convertible Perpetual Preferred Stock to $2.4444. The adjustment resulted from C3is’s 1-for-40 reverse stock split of its common stock effective August 19, 2026 and related warrant exercise price adjustments through August 26, 2026. Imperial Petroleum states it acquired its position in connection with a spin-off distribution and plans to review its investment on an ongoing basis, with flexibility to buy more, hold, or sell shares depending on business, market and other factors.

Filing Explained

The amendment preserves the disclosed 80.5% voting and dispositive position while reporting no new Common Stock trade or completed corporate action.

The filing reports no additional Common Stock transaction during the past 60 days beyond the conversion-price and warrant adjustments described; it therefore updates the ownership record rather than documenting a new purchase or sale.

Imperial and relevant parties may discuss matters ranging from operations to extraordinary corporate transactions, while reserving the right to change their intentions; this is a stated possibility, not a disclosed transaction or agreement.

A later filing would be needed to establish an actual acquisition, sale, or implemented corporate action; this amendment itself reports none.

Key Figures

Shares beneficially owned: 6,136,475 shares of Common Stock Percent of class beneficially owned: 80.5% Conversion price of Series A Convertible Preferred Stock: $2.4444 per share +4 more

7 metrics

Shares beneficially owned 6,136,475 shares of Common Stock Beneficially owned by Imperial Petroleum Inc. with sole voting and dispositive power

Percent of class beneficially owned 80.5% Portion of C3is Inc. common stock class represented by 6,136,475 shares

Conversion price of Series A Convertible Preferred Stock $2.4444 per share Adjusted pursuant to terms of 5.0% Series A Cumulative Convertible Perpetual Preferred Stock

Reverse stock split ratio 1-for-40 Reverse stock split of C3is common stock effective August 19, 2026

Date reverse stock split became effective August 19, 2026 Effective date of 1-for-40 reverse stock split of common stock

End of warrant adjustment period August 26, 2026 End of adjustment period for Class B-1, B-2, C-1 and C-2 Warrants

Shares owned by Harry N. Vafias 19 shares of Common Stock Beneficially owned, including through Arethusa Properties LTD and Flawless Management, Inc.

Key Terms

beneficially owned, sole voting power, reverse stock split, Cumulative Convertible Perpetual Preferred Stock, +1 more

5 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: | 7 | Sole Voting Power 6,136,475.00"

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.

reverse stock split financial

"as a result of the Issuer's 1-for-40 reverse stock split of its Common Stock"

A reverse stock split reduces a company's number of outstanding shares while raising the price per share proportionally, so the total value of each investor's holding is unchanged; a 1-for-10 split turns 100 shares worth $1 each into 10 shares worth $10 each. Companies often do this to regain compliance with an exchange's minimum price rule or to attract investors who avoid very low-priced stocks.

Cumulative Convertible Perpetual Preferred Stock financial

"5.0% Series A Cumulative Convertible Perpetual Preferred Stock, par value $0.01 per share"

A cumulative convertible perpetual preferred stock is a hybrid investment that behaves like a long‑term share paying regular fixed payouts, where any missed payments pile up and must be paid later (cumulative), can be switched into common shares under set rules (convertible), and has no fixed maturity date (perpetual). It matters to investors because it offers steadier income and higher payout priority than common stock while preserving the potential upside of converting to ordinary shares, though conversion can dilute existing owners—think of it as a mix between a bond’s steady coupons and a stock’s growth option.

warrants financial

"adjustment of the exercise price of the Class B-1, B-2, C-1 and C-2 Warrants of the Issuer"

Warrants are special documents that give you the right to buy a company's stock at a set price before a certain date. They are often used as a way for companies to attract investors or raise money, and their value can increase if the company's stock price goes up.

Stock Split

1-for-40 reverse split · Effective August 19, 2026

Split Ratio 1-for-40 reverse split

Effective Date August 19, 2026

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many C3is Inc. (CISS) shares does Imperial Petroleum currently beneficially own?

Imperial Petroleum beneficially owns 6,136,475 shares of C3is Inc. common stock, with sole voting and dispositive power over all of these shares. This stake represents 80.5% of C3is’s outstanding common stock as reported in the Schedule 13D/A (Amendment No. 13).

What percentage of C3is Inc. (CISS) does Imperial Petroleum control after this amendment?

Imperial Petroleum reports beneficial ownership of 80.5% of C3is Inc.’s outstanding common stock. It holds sole voting and sole dispositive power over its 6,136,475 shares, indicating effective control of a substantial majority of the company’s common equity.

Why did Imperial Petroleum file Amendment No. 13 to its Schedule 13D for C3is Inc. (CISS)?

Amendment No. 13 was filed to update the number and percentage of C3is common shares beneficially owned by Imperial Petroleum after the conversion price of the Series A Convertible Preferred Stock was adjusted to $2.4444 following a 1-for-40 reverse stock split and related warrant adjustments.

What corporate action did C3is Inc. (CISS) take that affected Imperial Petroleum’s reported holdings?

C3is effected a 1-for-40 reverse stock split of its common stock, effective August 19, 2026. This triggered an adjustment of the conversion price of its Series A Convertible Preferred Stock to $2.4444 and related warrant exercise price adjustments through August 26, 2026, prompting the updated ownership disclosure.

Does Imperial Petroleum plan to change its investment in C3is Inc. (CISS)?

Imperial Petroleum states it will review its investment on a continuing basis and may acquire additional C3is securities, or retain or sell some or all of its shares, through open-market trades, block trades, underwritten offerings or private transactions, depending on business, market and other listed factors.

Who from Imperial Petroleum serves on the board of C3is Inc. (CISS)?

Harry N. Vafias, Chairman, CEO and President of Imperial Petroleum, serves as Non-Executive Chairman of C3is and beneficially owns 19 C3is common shares (including through Arethusa Properties LTD and Flawless Management, Inc.). Directors John Kostoyannis and George Xiradakis also sit on C3is’s board and each own nil C3is shares.

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

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Available on EDGAR 08/28/2026 - 07:00 PM EDT Accepted by SEC EDGAR 08/28/2026 - 07:00 PM EDT Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 13)

C3is Inc.

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

Y18284409

(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)

08/26/2026

(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): Y18284409

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 6,136,475.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 6,136,475.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

6,136,475.00

12

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

13

Percent of class represented by amount in Row (11)

80.5 %

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. 13 (this "Amendment No. 13") 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, Amendment No. 11 filed on June 24, 2026 and Amendment No. 12 filed on July 30, 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. 13 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 $2.4444 pursuant to the terms of the Series A Convertible Preferred Stock as a result of the Issuer's 1-for-40 reverse stock split of its Common Stock, effective August 19, 2026, and the related adjustment of the exercise price of the Class B-1, B-2, C-1 and C-2 Warrants of the Issuer during the adjustment period applicable to such warrants, which ended August 26, 2026. This Amendment No. 13 is also being filed to update the percentage of shares of Common Stock of the Issuer beneficially owned by Imperial Petroleum to reflect change in percentage ownership based on the revised total number of outstanding shares of Common Stock. 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 19 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:	08/28/2026