Count Giselbert (or Gilbert) of Loon or (later) Duras (d. before 1138), was the deputy advocate (subadvocatus) of Saint Trudo’s Abbey. He was son of Otto I, Count of Duras, and his wife Oda. Giselbert was the first person to be named in contemporary documents as a count of Duras.

Giselbert was involved in several conflicts which involved the abbey, as mentioned in several parts in the Abbey's Gesta or chronicle.

Apart from the Gesta, much of what we know about Giselbert is from the charters that he witnessed, which also gives insight as to his relationship with the Counts of Namur, a family into which he eventually married.^{[clarification needed]} Emperor Henry IV confirmed donations made by Henry I, Count of Durbuy, son of Albert II, Count of Namur, to the Church of Saint James in Liège, as witnessed by Giselbert. The emperor also confirmed the claim of Albert’s family to Saint Begga's Collegiate Church in Andenne.

Giselbert married twice. His first wife was Gertrud, of unknown parentage. His second wife was Oda, daughter of Otto II, Count of Chiny, and his wife Alix, daughter of Albert III, Count of Namur. Giselbert and Gertrud had eight children:

• Otto II, Count of Duras
• Conan of Duras^{[citation needed]} (Appears in Wolters 19th century writer, who cites Mantelius and Butkens, 17th century writers)
• Giselbert of Duras
• Gerard (d. 1174), Abbot of Saint Trudo’s
• Thierry (d. 1183 or after), Archdeacon of Liège
• Bruno (d. 1177 or after), Canon at Liège, Saint Lambert
• Unnamed daughter, mother of Alexander II, Bishop of Liège (1164-1167)^{[citation needed]}
• Unnamed daughter, mother of Arnulf van Kortessem.^{[citation needed]}

Wolters identifies Julienne, daughter of Otto II, as an additional daughter of Giselbert and Gertrud, but this is unlikely as her husband and their sons inherited the countship of Duras. Upon his death, Giselbert was succeeded as Count of Duras by his son Otto.