The accident happened on Sunrise Highway, near Route 110, in Amityville at about 6:40 Monday morning.
There were no children aboard the bus when it crashed into the tanker. The tanker was carrying 5,700 gallons of waste oil.
Suffolk County police say the bus driver, 56-year-old Piters Calixte, was airlifted to Stony Brook University Hospital.
The driver of the oil tanker was not injured. No oil leaked from the tanker.
Authorities are conducting safety inspections of both vehicles.