Oliver first appeared as Bishop of Syrmia (Hungarian: Szerém, Serbian: Srem) in a contemporary document on 6 November 1250,[1] when donated the village of Dras (Drasch) to Lawrence Becsegergely, the provost of Szenternye (present-day a borough of Sremska Mitrovica, Serbia).
Oliver's name was involved in the list of barons and prelates in the royal charter of Béla IV of Hungary, issued on 28 June 1254.
[2] Oliver intended to resign from his position and join the Franciscan Order due to his poor health and "severe fatigue of his body" in 1262.
As a result, he sent his two clergymen, treasurer Thomas and canon Peter to the Roman Curia to ask for his acquittal from Pope Urban IV.
In response, the pope wrote a letter to Oliver's metropolitan, Archbishop Smaragd of Kalocsa in December 1262, and ordered him to investigate the circumstances and if he sees fit, accept the resignation of Oliver, absolve him from the obligation to govern the diocese and allow him to join the Franciscan monks.