Welsh detectives are warning owners of Mercedes vans to keep an eye on their vehicles after 24 thefts in just 23 days.
Gwent Police said criminals have been targeting Benz Sprinter models for their exhaust systems and catalytic converters.
Inspector Carl Williams described the rise in incidents since September 30 as rapid - with most occurring during night time.
He said: "Catalytic converters are composed of several metals, some include small amounts of precious metals such as platinum and palladium, making them a target for criminals.
"We are currently investigating each reported crime and asking owners of Mercedes-Benz Sprinter vans to secure their vehicles and remain alert.
"Steps that can be taken to prevent this type of crime include parking vehicles in well-lit, open areas and installing CCTV camera systems."
Officers also said van owners should also consider etching a catalytic converter with a serial number as well as fitting them with protective sleeves.
Full details of each incident can be found on Gwent Police's website. Anyone with information is asked to call 101 or Crimestoppers on 0800 555111.