The exact nature of the relics is not specified in the most reliable contemporary sources. According to Orderic Vitalis – an Anglo-French monk who was writing more than half a century later, but who had been brought up in a Norman monastery – Harold swore on super sanctissimus reliquias juraverat, generally translated as "saint's relics". Anglo-Saxon sources from the 1060s are completely silent on the subject, however, and it's as possible to argue that the entire story of Harold's oath was an invention of the Norman propaganda machine, used to justify William's invasion, as it is to suppose that the Saxon chronicles deliberately suppressed an incident discreditable to one of their own. Elizabeth van Houts, in her 1992 edition of William of Jumieges's Gesta Normannorum Ducum, argues that the entire story is based on a single, official, Norman account, drawn up to be presented to the Pope in order to justify and seek approval for the invasion. Even Norman sources suggest there was an element of deception involved - that Harold only realised too late the holyness of the oath he'd sworn because the presence of the relics was concealed from him.

That said, some later sources are more specific. The Brevis Relatio, written by a monk of Battle Abbey around 1130, the Warenne Chronicle (about 1157) and Wace (a canon at Bayeux), writing after 1155, say one of the reliquaries was the "ox eye" or "bull's eye". Wace's passage says that William "ordered that all the holy relics be assembled in one place, having an entire tub filled with them; then he ordered them covered with a silk cloth so that Harold neither knew about them nor saw them, nor was it pointed out to him. On top of it he placed a reliquary, the finest he could choose and the most precious he could find; I have heard it called 'ox-eye'." Apparently this was because the centre of the reliquary was an elaborate mounting for a magnificent gemstone.

If this identification is accepted then the relics may have been those of St Pancras, which the Warenne Chronicle explicitly identifies with the ox-eye reliquary. Pancras, a Roman citizen of Diocletian's reign, was especially venerated in England because St Augustine had been despatched from Rome bearing some of his relics when he was sent to convert the Saxons. However, the cult of St Pancras was unknown in Normandy, which perhaps suggests that Warenne was wrong, and implies that it was more likely that any oath was sworn on locally venerated relics.

If so, then much depends on where exactly an oath may have been sworn. There is no agreement on this point. Orderic says Rouen, William of Poitiers says Bonneville-sur-Toques, and the Bayeux Tapestry puts it in Bayeux. Stephen D. White, in his "Locating Harold's oath and tracing his itinerary" in Pastan and White [eds] The Bayeux Tapestry and its Contexts, takes this latter identification and uses it to suggest that the most likely candidate is the bones of Saints Rasyphus and Ravennus. He argues that Duke William's brother, Bishop Odo of Bayeux, is known to have commissioned a new reliquary to hold these c.1050 which can be identified with the image of the reliquary shown on the Bayeux Tapestry.

However, Odo's name is not associated with this stage of the tapestry narrative, meaning it's difficult to establish who exactly selected the reliquaries for any oath that was sworn. There's no way to be certain, but if the incident occurred, and if it occurred at Bayeux, then most likely Odo would have been involved. As such, White's identification, while it must be considered tentative, is certainly not implausible.