Police in the Nelson-Tasman region are concerned by a spate of 50 fuel thefts in the area in the past few months.
They say thieves have siphoned off fuel from industrial machinery and entered properties to take fuel from farm vehicles, storage tanks and cars.
Police say the largest single theft was 1500 litres of aviation gas in a tanker taken from Motueka airport.
The most recent incident was on 17 July when an attempt was made to steal diesel from a property in Hope and the owner's labrador was found dead.
Sergeant Dave Prentice says if the thieves were responsible for the dog's death, it raises concerns about what they might do next.