- O'BRIEN HR LTD- SC802227 - Incorporated on 8 March 2024 
- O'BRIEN S &CO LTDActive - Proposal to Strike off- 10281627 - Incorporated on 15 July 2016 
- O’BRIEN PM LTD- 15405176 - Incorporated on 11 January 2024 
- NIC O'BRIEN LTDDisolved- 14427080 - Dissolved on 26 March 2024 
- SUE O'BRIEN LTDDissolved- 08253402 - Dissolved on 4 December 2018 
- O'BRIENS EA LTDDissolved- 10201503 - Dissolved on 5 November 2019 
- TL O'BRIENS LTDLiquidation- NI066619 - Incorporated on 16 October 2007 
- JON O'BRIEN LTDDissolved- 05841104 - Dissolved on 16 October 2012 
- TOM BRIEN LTDDissolved- 07441589 - Dissolved on 7 May 2019 
- TOM O'BRIEN LTD- 13811412 - Incorporated on 21 December 2021 
- DR. COLM O'BRIENActive - Proposal to Strike off- NI605394 
- O'BRIEN NDT LTDDisolved- 07607804 - Dissolved on 6 September 2022 
- JOE O'BRIEN LTD- 12183141 - Incorporated on 2 September 2019 
- BRIENNE LTDDisolved- 14147731 - Dissolved on 16 April 2024 
- BRIENOU LTDActive - Proposal to Strike off- 13387120 - Incorporated on 11 May 2021 
- R.J. O'BRIEN (EUROPE) LIMITED- 07432813 - Incorporated on 8 November 2010 
- O'BRIEN LIMITED- 03126206 - Incorporated on 15 November 1995 
- EDWARD O'BRIENLiquidation- 00136509 - Incorporated on 18 June 1914 
- HALL & O'BRIEN LTD- 15008520 - Incorporated on 17 July 2023 
- LANA T O'BRIEN LTD- 07290610 - Incorporated on 21 June 2010