Imperial Petroleum (CISS) reports 90.2% beneficial ownership in C3is

Rhea-AI Filing Summary

Imperial Petroleum Inc. filed Amendment No. 10 to its Schedule 13D, updating its beneficial ownership in C3is Inc.. The company reports beneficial ownership of 4,994,672 shares of common stock, representing 90.2% of the class.

The update reflects changes in the conversion price of C3is’s 5.0% Series A Cumulative Convertible Perpetual Preferred Stock to $3.0032 after a 1-for-7 reverse stock split of the common stock effective April 27, 2026 and related warrant price adjustments. Imperial Petroleum states it may buy more, hold, or sell C3is shares over time based on business, market, and strategic factors.

Key Figures

Beneficial ownership: 4,994,672 shares Ownership percentage: 90.2% Conversion price: $3.0032 +3 more

6 metrics

Beneficial ownership 4,994,672 shares Imperial Petroleum beneficially owned C3is common stock

Ownership percentage 90.2% Percent of C3is common stock class represented by Imperial Petroleum’s holdings

Conversion price $3.0032 Adjusted conversion price of 5.0% Series A Convertible Preferred Stock after reverse split

Reverse stock split ratio 1-for-7 C3is common stock reverse split effective April 27, 2026

Series A coupon 5.0% Rate on C3is Series A Cumulative Convertible Perpetual Preferred Stock

Harry N. Vafias personal holdings 718 shares C3is common stock beneficially owned by Harry N. Vafias

Key Terms

beneficially owned, 1-for-7 reverse stock split, 5.0% Series A Cumulative Convertible Perpetual Preferred Stock, Class B-1, B-2, C-1 and C-2 Warrants, +1 more

5 terms

beneficially owned financial

"This Amendment No. 10 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.

1-for-7 reverse stock split financial

"as a result of the Issuer's 1-for-7 reverse stock split of its Common Stock, effective April 27, 2026"

5.0% Series A Cumulative Convertible Perpetual Preferred Stock financial

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

Class B-1, B-2, C-1 and C-2 Warrants financial

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

Spin-Off Distribution financial

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

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 10)

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)

05/04/2026

(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 4,994,672.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 4,994,672.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

4,994,672.00

12

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

13

Percent of class represented by amount in Row (11)

90.2 %

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. 10 (this "Amendment No. 10") 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 and Amendment No. 9 filed on February 4, 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. 10 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 $3.0032 pursuant to the terms of the Series A Convertible Preferred Stock as a result of the Issuer's 1-for-7 reverse stock split of its Common Stock, effective April 27, 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 May 4, 2026. This Amendment No. 10 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, including to reflect the issuance of shares by the Company. 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 718 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:	Harry N. Vafias
Name/Title:	Chief Executive Officer
Date:	05/06/2026

FAQ

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

Imperial Petroleum reports beneficial ownership of 4,994,672 C3is common shares, representing 90.2% of the class. This high percentage indicates effective control of C3is, although the filing focuses on updating ownership figures rather than announcing a new acquisition.

Why did Imperial Petroleum file Amendment No. 10 to its Schedule 13D on C3is (CISS)?

Amendment No. 10 was filed to update the number and percentage of C3is shares Imperial Petroleum beneficially owns. The changes arise from adjustments to the preferred stock conversion price and warrants following C3is’s 1-for-7 reverse stock split and subsequent share issuances by the company.

How did C3is’s reverse stock split affect Imperial Petroleum’s CISS holdings?

C3is implemented a 1-for-7 reverse stock split of its common stock effective April 27, 2026. Under the Series A preferred terms, this triggered an adjustment of the conversion price to $3.0032 and related warrant exercise prices, which in turn affected Imperial Petroleum’s beneficial ownership calculations.

What securities drive Imperial Petroleum’s beneficial ownership in C3is (CISS)?

Imperial Petroleum’s beneficial ownership stems from C3is’s 5.0% Series A Cumulative Convertible Perpetual Preferred Stock and related warrants. Changes in the conversion price and warrant exercise prices, together with C3is share issuances, led to the revised 4,994,672-share, 90.2% ownership figure disclosed in the amendment.

What future actions does Imperial Petroleum contemplate regarding its C3is (CISS) investment?

Imperial Petroleum states it will continuously review its C3is investment and may buy additional securities, retain its holdings, or sell some or all shares. Possible transactions include open-market trades, block trades, underwritten offerings, or private deals, depending on business, market, tax, and strategic considerations.

Do Imperial Petroleum insiders hold C3is (CISS) shares personally?

Chairman and CEO Harry N. Vafias beneficially owns 718 C3is common shares, including through Arethusa Properties LTD and Flawless Management, Inc. Directors John Kostoyannis and George Xiradakis serve on C3is’s board as well, but each is reported as owning nil C3is common shares as of the filing date.