Oscar Silva is a pharmacy assistant at Princeton-Plainsboro Teaching Hospital. He appeared in the episode 5 to 9 where he discovered that extra ephedrine had been shipped to the hospital. He was portrayed by actor Jeremy Howard.
Oscar's discovery of extra shipments led to the discovery that one of the other pharmacy assistants, Gail, had regularly double-ordered controlled drugs that she then covered up by removing them from the hospital but reconciling the receipts with the original single orders.
Oscar is also shown in the Nurse Jeffrey episodes where Nurse Jeffrey attempts to get Oscar to admit that House has been stealing drugs from the hospital's pharmacy. However, Oscar denied that this had ever happened as, if it did, there would be massive amounts of paperwork and, if the paperwork hadn't been done, someone would have been fired. It is in the episode that Oscar's last name is revealed.