Manx Police are investigating the theft of what is described as a "substantial amount" of oil from a house in Douglas.
The oil was siphoned from a tube attached to the tank on Demesne Road and stolen between 16 February and Wednesday.
Officers said the thieves would have needed a large container and vehicle to transport the fuel, as well as causing lots of noise.
Anyone who witnessed the theft is urged to contact Manx Police.
