Thomas Siebel’s net worth over time
Only dates with a published estimate are shown. Nothing is filled in between. Tap or hover a bar to see the source.
See the numbers as a table
| Date | Estimate | Source |
| 2019 | $2.9 billion | Forbes World's Billionaires List 2019 |
| 2020 | $3.6 billion | Forbes World's Billionaires List 2020 |
| 2021 | $4.9 billion | Forbes World's Billionaires List 2021 |
| 2022 | $3.5 billion | Forbes World's Billionaires List 2022 |
| 2023 | $3.5 billion | Forbes World's Billionaires List 2023 |
| 2024 | $3.9 billion | Forbes World's Billionaires List 2024 |
| 2025 | $4.1 billion | Forbes World's Billionaires List 2025 |
| 2026 | $3.9 billion | Forbes World's Billionaires List 2026 |
| Oct 2026 | $4.6 billion | Forbes Real-Time Billionaires · Forbes real-time estimate |
Where the money comes from
These are the main sources of wealth named in the reporting we cite. No published source breaks the total into exact amounts, so we do not show percentages.
Thomas Siebel’s fortune in real-life terms
Based on the Forbes Real-Time Billionaires estimate above. Median full-time U.S. pay is $65,416 a year ($1,258 a week, BLS, Q2 2026), before taxes. Typical (median) U.S. family net worth is $216,100 (Federal Reserve, 2025 Survey of Consumer Finances).
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Thomas Siebel has an estimated net worth of $4.6 billion, according to Forbes Real-Time Billionaires, Thomas Siebel profile (figures as of October 20, 2026). That is up from $2.9 billion in 2019.
Thomas Siebel is a United States software entrepreneur in the technology industry. He is best known for founding Siebel Systems and later starting C3.ai, where he has served as founder, chairman, and CEO. Before that, he worked at Oracle from 1984 to 1990 in management roles and was also CEO of Gain Technology. His career centered on business software, especially tools used by large companies to manage sales, customer relationships, and enterprise data.
His fortune came from building and selling software companies. After leaving Oracle in 1990, he launched Siebel Systems and turned it into a major customer relationship management company. Oracle later bought Siebel Systems in 2006 for $5.8 billion in cash and stock. In 2009, he created C3.ai, an enterprise AI company that started as a clean energy firm. He took C3.ai public in 2020 at a near $10 billion valuation, adding another major source of wealth.
How Thomas Siebel makes money
Most of Thomas Siebel’s wealth comes from software. He built Siebel Systems after leaving Oracle, where he had worked as a salesman and executive. Siebel Systems focused on customer relationship management software for large businesses. The company grew quickly, and Oracle acquired it in 2006 for $5.8 billion in cash and stock. That deal was a key turning point in his career and remains one of the biggest events tied to his fortune.
His later wealth has been tied to C3.ai, the enterprise AI company he created in 2009. The business first focused on clean energy, then briefly used the name C3IoT in 2016 as it pursued the internet of things market. In 2020, Siebel took C3.ai public at a near $10 billion valuation. Alongside his business holdings, he has also put large sums into philanthropy, giving more than $150 million to the University of Illinois Urbana-Champaign.
Forbes net worth timeline
Forbes has tracked big swings in Siebel’s fortune in recent years. It estimated his net worth at $2.9 billion in 2019, then $3.6 billion in 2020, and $4.9 billion in 2021. The next 2 yearly lists were lower at $3.5 billion in 2022 and $3.5 billion in 2023. Those changes fit a career built around large software holdings, with C3.ai and the legacy value of Siebel Systems shaping how his wealth moved.
The estimate later moved higher again. Forbes put him at $3.9 billion in 2024 and $4.1 billion in 2025. On Forbes’ real-time billionaires tracker, he stood at $4.6 billion as of October 20, 2026. Forbes places him in technology and ties his wealth to business software. That makes sense given the 2 companies most associated with his fortune: Siebel Systems, which Oracle bought, and C3.ai, which he led to the public market.
Career and money timeline
- 1984
He joined Oracle and held several management roles.
- 1992
Gain Technology merged with Sybase in December.
- 2005
Oracle acquired Siebel Systems.
- 2009
He created enterprise AI firm C3.ai.
- 2020
He took C3.ai public at a near $10 billion valuation.
- 2024
He made a gift to help build the Siebel School of Computing and Data Science.
Thomas Siebel net worth FAQ
What is Thomas Siebel's net worth?
Thomas Siebel's net worth is an estimated $4.6 billion, according to Forbes Real-Time Billionaires, Thomas Siebel profile (October 20, 2026). It is an estimate, not an official figure.
How did Thomas Siebel get so rich?
The main sources named in the reporting we cite are: Business software.
Is Thomas Siebel a billionaire?
Yes. Forbes Real-Time Billionaires estimates Thomas Siebel is worth $4.6 billion.
How has Thomas Siebel's net worth changed?
The earliest published estimate we track is $2.9 billion (2019, Forbes World's Billionaires List 2019). The latest is $4.6 billion (October 20, 2026).
What company made Thomas Siebel famous?
Siebel Systems made him a major name in enterprise software. Oracle bought the company in 2006 for $5.8 billion in cash and stock.
What is Thomas Siebel’s net worth according to Forbes?
Forbes' real-time billionaires tracker put him at $4.6 billion as of October 20, 2026.
Sources
- Forbes Real-Time Billionaires, Thomas Siebel profile (October 20, 2026)
- Forbes World's Billionaires List 2019, Thomas Siebel profile (March 5, 2019)
- Forbes World's Billionaires List 2020, Thomas Siebel profile (April 8, 2020)
- Forbes World's Billionaires List 2021, Thomas Siebel profile (April 6, 2021)
- Forbes World's Billionaires List 2022, Thomas Siebel profile (April 5, 2022)
- Forbes World's Billionaires List 2023, Thomas Siebel profile (April 4, 2023)
- Forbes World's Billionaires List 2024, Thomas Siebel profile (April 2, 2024)
- Forbes World's Billionaires List 2025, Thomas Siebel profile (April 2025)
- Forbes World's Billionaires List 2026, Thomas Siebel profile (March 10, 2026)
- U.S. Bureau of Labor Statistics, Usual Weekly Earnings (Q2 2026) (July 2026)
- Federal Reserve, 2025 Survey of Consumer Finances (median family net worth, Table 4) (October 2026)
- Background facts: Wikipedia, Thomas Siebel (accessed October 21, 2026). Used for career facts only, never for figures.
Photo: C3 Energy, CC BY-SA 1.0, via Wikimedia Commons.
Every number on this page is an estimate published by the source named next to it. We never fill in years with our own guesses. How we handle estimates.