![Callen John O'Brien](data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="%231b1b1b" class="bi bi-person-fill" viewBox="0 0 16 16"><path d="M3 14s-1 0-1-1 1-4 6-4 6 3 6 4-1 1-1 1zm5-6a3 3 0 1 0 0-6 3 3 0 0 0 0 6"/></svg>)
Callen John O'Brien
Chairman at
GBST HOLDINGS LIMITED
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Latest insider transactions
| Date | Company | Type | Amount | Volume |
| 26/05/2026 | Nova Dynamics | Buy | 1 250 000 $ | 32 000 |
| 21/05/2026 | Helios Materials | Sell | 845 000 $ | 19 500 |
| 14/05/2026 | Atlas Renewables | Buy | 2 030 000 $ | 48 200 |
Estimated holdings
| Company | Stake | Value |
| Nova Dynamics | 4.8 % | 18 400 000 $ |
| Helios Materials | 2.1 % | 6 950 000 $ |
| Atlas Renewables | 1.3 % | 3 280 000 $ |
| BluePeak Logistics | 0.9 % | 2 040 000 $ |
Related news feed
An executive increases exposure to an industrial stock
Sector rotation: insiders are more active on clean energy names
New regulatory filing published for executive transactions
Professional network
Executive Management
Board of Directors
Audit Committee
Institutional Investors
Sell-side Analysts
Career timeline
2026 - Chairman of the Board
2022 - Chief Executive Officer
2018 - Chief Financial Officer
2012 - Strategy Committee Member
- Stock Market
- Insiders
- Callen John O'Brien
- Insider transactions
