The 26-year-old's previous deal at Upton Park had been due to expire at the end of the current season.
However, having proved his worth during his 16 Premier League appearances so far this campaign, manager Sam Allardyce has decided to offer the defender extended terms until 2016.
O'Brien was one of Allardyce's first signings as West Ham boss back in July 2011.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Liverpool | 11 | 9 | 1 | 1 | 21 | 6 | 15 | 28 |
| 2 | Manchester CityMan City | 12 | 7 | 2 | 3 | 22 | 17 | 5 | 23 |
| 3 | Chelsea | 12 | 6 | 4 | 2 | 23 | 14 | 9 | 22 |
| 4 | Arsenal | 12 | 6 | 4 | 2 | 21 | 12 | 9 | 22 |
| 5 | Brighton & Hove AlbionBrighton | 12 | 6 | 4 | 2 | 21 | 16 | 5 | 22 |
| 6 | Tottenham HotspurSpurs | 12 | 6 | 1 | 5 | 27 | 13 | 14 | 19 |
| 7 | Nottingham ForestNott'm Forest | 12 | 5 | 4 | 3 | 15 | 13 | 2 | 19 |
| 8 | Aston Villa | 12 | 5 | 4 | 3 | 19 | 19 | 0 | 19 |
| 9 | Newcastle UnitedNewcastle | 11 | 5 | 3 | 3 | 13 | 11 | 2 | 18 |
| 10 | Fulham | 12 | 5 | 3 | 4 | 17 | 17 | 0 | 18 |
| 11 | Brentford | 12 | 5 | 2 | 5 | 22 | 22 | 0 | 17 |
| 12 | Manchester UnitedMan Utd | 11 | 4 | 3 | 4 | 12 | 12 | 0 | 15 |
| 13 | Bournemouth | 12 | 4 | 3 | 5 | 16 | 17 | -1 | 15 |
| 14 | West Ham UnitedWest Ham | 11 | 3 | 3 | 5 | 13 | 19 | -6 | 12 |
| 15 | Everton | 12 | 2 | 5 | 5 | 10 | 17 | -7 | 11 |
| 16 | Leicester CityLeicester | 12 | 2 | 4 | 6 | 15 | 23 | -8 | 10 |
| 17 | Wolverhampton WanderersWolves | 12 | 2 | 3 | 7 | 20 | 28 | -8 | 9 |
| 18 | Crystal Palace | 12 | 1 | 5 | 6 | 10 | 17 | -7 | 8 |
| 19 | Ipswich TownIpswich | 11 | 1 | 5 | 5 | 12 | 22 | -10 | 8 |
| 20 | Southampton | 11 | 1 | 1 | 9 | 7 | 21 | -14 | 4 |
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