Company: RIG
Filing Date: 2025-09-26
Form Type: 424B5
Source: 0001451505-25-000102
Chunk: 5

Company: Transocean Ltd.
Filing Date: 2025-09-26
Form: 424B5
Chunk 5
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, which are available free of charge on the SEC website at www.sec.gov. |

S-iv

The foregoing risks and uncertainties are beyond our ability to control, and in many cases, we cannot predict the risks and uncertainties that could cause our actual results to differ materially from those indicated by the forward-looking statements. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those indicated. All subsequent written and oral forward-looking statements attributable to us or to persons acting on our behalf are expressly qualified in their entirety by reference to these risks and uncertainties. You should not place undue reliance on forward-looking statements, each of which speaks only as of the date of the particular statement. We expressly disclaim any obligations or undertaking to release publicly any updates or revisions to any forward-looking statement to reflect any change in our expectations or beliefs with regard to the statement or any change in events, conditions or circumstances on which any forward-looking statement is based, except as required by law.

<div align='center'>S-v</div>

### SUMMARY
This summary highlights information contained elsewhere in this prospectus supplement and the accompanying base prospectus, or incorporated by reference in this prospectus supplement and the accompanying base prospectus. As a result, this summary does not contain all of the information that may be important to you or that you should consider before investing in our shares. You should carefully read this entire prospectus supplement and the accompanying base prospectus, together with all documents incorporated by reference herein and therein, which are described under “Incorporation by Reference” in this prospectus supplement.

#### About Transocean Ltd.
We are a leading international provider of offshore contract drilling services for oil and gas wells. As of September 19, 2025, we owned or had partial ownership interests in and operated a fleet of 27 mobile offshore drilling units, consisting of 20 ultra-deepwater floaters and seven harsh environment floaters.

We provide, as our primary business, contract drilling services in a single operating segment, which involves contracting our mobile offshore drilling rigs, related equipment and work crews to drill oil and gas wells. We specialize in technically demanding regions of the global offshore drilling business with a particular focus on ultra-deepwater and harsh environment drilling services. Our drilling fleet is one of the most versatile fleets in the world, consisting of drillships and semisubmersible floaters used in support of offshore drilling activities and offshore support services on a worldwide basis.

We perform contract drilling services by