While the cause of the outbreak that left at least 55 students vomiting and with diarrhea so bad they missed seminars and lectures had not been pinpointed, fingers were being pointed straight at the food served at the tony Feb. 2 event, The Daily Telegraph reported Monday.
"Mansfield Ball was excellent," one student who attended told the University newspaper the Oxford Student, "and it's a shame that so many of us have been poisoned."
He added it was "fairly apparent" students were "suffering from food poisoning caused by a bad batch of oysters."
The website for the ball said attendees would experience "a lavish banquet, accompanied by fine wines and the soothing sounds of harp music."
Mansfield Ball President Anna Ploszajski confirmed students had fallen ill after the event.
"There have been allegations of food poisoning," she said. "It appears to be the seafood bar that has come under questioning.
"Mansfield College [officials] are carrying out a full investigation into the possible cause of the illness and until the investigation is complete, I am unable to offer a suggestion as to what has brought on the symptoms.
"This unfortunate incident should not, and will not, belittle the achievement of what has been the culmination of almost two years of preparation.
"The event has consistently been trumpeted as unquestionably the most successful ball in Mansfield's history."
University chiefs ordered an investigation and government health officials were looking into the matter, the Telegraph said.