Company: RIG
Filing Date: 2025-09-26
Form Type: 424B5
Source: 0001451505-25-000102
Chunk: 0

Company: Transocean Ltd.
Filing Date: 2025-09-26
Form: 424B5
Chunk 0
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Filed Pursuant to Rule 424(b)(5)
Registration No. 333-280617 Prospectus Supplement
(To Prospectus dated June 28, 2024) Transocean Ltd. 125,000,000 Shares We are offering to sell 125,000,000 of our shares, par value $0.10 (“shares”). Our shares are listed on the New York Stock Exchange (“NYSE”) under the symbol “RIG.” The last reported sale price of our shares on the NYSE on September 22, 2025 was $3.39 per share.

| ​                                | ​ | Per Share |      | ​ | ​ |     | Total |             |   | ​ |
|:---------------------------------|:--|:----------|-----:|:--|:--|:----|:------|------------:|:--|:--|
| Price to the public              | ​ | $         | 3.05 | ​ | ​ |     | $     | 381,250,000 | ​ |   |
| Underwriting discount(1)         | ​ | $         | 0.12 | ​ | ​ |     | $     |  15,000,000 | ​ |   |
| Proceeds, before expenses, to us | ​ | $         | 2.93 | ​ | ​ |     | $     | 366,250,000 | ​ |   |

__________ (1) Please read “Underwriting (Conflicts of Interest)” for additional information regarding underwriting compensation. An affiliate of one of our directors, Frederik Mohn, has provided an indication of interest in purchasing up to an aggregate of 4,000,000 shares from the underwriters at the public offering price.The number of our shares available for sale to the public will be reduced to the extent such person purchases such shares. The underwriters will not receive any underwriting discounts or commissions on any shares sold to any affiliate of Frederik Mohn. The indication of interest is not a commitment to purchase, and such person is not obligated to purchase any of our shares in this offering. Please read “Underwriting” for additional information. We have granted the underwriters an option for a period of 30 days to purchase up to an additional 18,750,000 of our shares at the public offering price, less underwriting discounts and commissions. INVESTING IN OUR SHARES INVOLVES RISKS. PLEASE READ THE “RISK FACTORS