Company: RIG
Filing Date: 2025-09-26
Form Type: 424B5
Source: 0001451505-25-000102
Chunk: 1

Company: Transocean Ltd.
Filing Date: 2025-09-26
Form: 424B5
Chunk 1
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” ON PAGE S-4 OF THIS PROSPECTUS SUPPLEMENT AND THE “RISK FACTORS” SECTION BEGINNING ON PAGE 9 OF OUR ANNUAL REPORT ON FORM 10-K FOR THE YEAR ENDED DECEMBER 31, 2024 , PAGE 24 OF OUR QUARTERLY REPORT ON FORM 10-Q FOR THE QUARTERLY PERIOD ENDED MARCH 31, 2025 AND PAGE 24 OF OUR QUARTERLY REPORT ON FORM 10-Q FOR THE QUARTERLY PERIOD ENDED JUNE 30, 2025 , WHICH ARE INCORPORATED BY REFERENCE INTO THIS PROSPECTUS SUPPLEMENT AND THE ACCOMPANYING BASE PROSPECTUS CONCERNING FACTORS YOU SHOULD CONSIDER BEFORE INVESTING IN OUR SHARES. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement and the accompanying base prospectus are truthful or complete. Any representation to the contrary is a criminal offense. The underwriters expect to deliver the shares on or about September 26, 2025. ____________________ Joint Book-Running Managers

| Citigroup    |                         | ​ | Morgan Stanley |                        |
| DNB Carnegie | Goldman Sachs & Co. LLC |   |                | Wells Fargo Securities |

Co-Managers

| SB1 Markets | ​ | Standard Bank |

The date of this prospectus supplement is September 24, 2025

S TABLE OF CONTENTS PROSPECTUS SUPPLEMENT ABOUT THIS PROSPECTUS SUPPLEMENT AND THE ACCOMPANYING BASE PROSPECTUS S- ii FORWARD-LOOKING INFORMATION S- iii SUMMARY S- 1 THE OFFERING S- 2 RISK FACTORS S- 4 USE OF PROCEEDS S- 6 DESCRIPTION OF TRANSOCEAN LTD. SHARES S- 7 MATERIAL TAX CONSEQUENCES S- 18 UNDERWRITING (CONFLICTS OF INTEREST) S- 27 LEGAL MATTERS S- 35 EXPERTS S- 35 WHERE YOU CAN FIND MORE INFORMATION S- 35 INCORPORATION BY REFERENCE S- 36

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| BASE PROSPECTUS                                                              |   ​ |
| ABOUT THIS PROSPECTUS                                                        |  ii |
| FORWARD-LOOKING INFORMATION                                                  | iii |
| ENFORCEABILITY OF CIVIL LIABILITIES AGAINST FOREIGN PERSONS                  |