| Game |
| Result | Moves |
Year | Event/Locale | Opening |
| 26. R Koster vs F Doettling |
| ½-½ | 29 | 2004 | Dutch Team Championship | A14 English |
| 27. V Chuchelov vs R Koster |
| 1-0 | 30 | 2004 | Dutch Team Championship | E17 Queen's Indian |
| 28. R Koster vs M Bosboom |
| ½-½ | 46 | 2004 | Amsterdam ACT op | E14 Queen's Indian |
| 29. Lobron vs R Koster |
| 1-0 | 50 | 2004 | Amsterdam ACT op | D87 Grunfeld, Exchange |
| 30. V Akopian vs R Koster |
| 1-0 | 44 | 2005 | Amsterdam Chess Tournament | E60 King's Indian Defense |
| 31. R Koster vs R Janssen |
| 0-1 | 42 | 2005 | Amsterdam Chess Tournament | D35 Queen's Gambit Declined |
| 32. R Koster vs Smeets |
| ½-½ | 32 | 2005 | Stork Young Masters | D30 Queen's Gambit Declined |
| 33. S Zhigalko vs R Koster |
| 1-0 | 32 | 2005 | Stork Young Masters | C02 French, Advance |
| 34. R Koster vs A Bitalzadeh |
| 1-0 | 61 | 2005 | Stork Young Masters | E90 King's Indian |
| 35. Nyback vs R Koster |
| 1-0 | 65 | 2005 | Stork Young Masters | A96 Dutch, Classical Variation |
| 36. R Koster vs J Michielsen |
| ½-½ | 45 | 2005 | Stork Young Masters | D10 Queen's Gambit Declined Slav |
| 37. R Koster vs B Michiels |
| 1-0 | 38 | 2005 | Stork Young Masters | A30 English, Symmetrical |
| 38. M Bensdorp-De Labaca vs R Koster |
| ½-½ | 67 | 2005 | Stork Young Masters | A96 Dutch, Classical Variation |
| 39. W Spoelman vs R Koster |
| ½-½ | 31 | 2005 | Stork Young Masters | B62 Sicilian, Richter-Rauzer |
| 40. R Koster vs I Vasilevich |
| 0-1 | 32 | 2005 | Stork Young Masters | D36 Queen's Gambit Declined, Exchange, Positional line, 6.Qc2 |
| 41. T Grooten vs R Koster |
| ½-½ | 33 | 2024 | Groningen Open | D11 Queen's Gambit Declined Slav |
| 42. R Koster vs P Hummel |
| 1-0 | 43 | 2024 | Groningen Open | E47 Nimzo-Indian, 4.e3 O-O 5.Bd3 |
| 43. S L Narayanan vs R Koster |
| 1-0 | 73 | 2024 | Groningen Open | A35 English, Symmetrical |
| 44. R Koster vs H Grooten |
| 1-0 | 39 | 2024 | Groningen Open | E42 Nimzo-Indian, 4.e3 c5, 5.Ne2 (Rubinstein) |
| 45. S Weber vs R Koster |
| 0-1 | 40 | 2024 | Groningen Open | B90 Sicilian, Najdorf |
| 46. R Koster vs A de Winter |
| 0-1 | 38 | 2024 | Groningen Open | A10 English |
| 47. S Albers vs R Koster |
| ½-½ | 21 | 2024 | Groningen Open | B90 Sicilian, Najdorf |
| 48. R Koster vs H Cernov |
| ½-½ | 23 | 2024 | Groningen Open | E47 Nimzo-Indian, 4.e3 O-O 5.Bd3 |
| 49. T Mareau vs R Koster |
| 0-1 | 21 | 2024 | Groningen Open | B23 Sicilian, Closed |
Kibitzing
