Theives have targeted vehicles belonging to businesses in Lichfield and Burntwood.
Police have warned firms to secure their fleets after two incidents in recent days.
Part of the exhaust was sawn off a Mitsubishi Shogun in Worthington Road, Lichfield, on the night of September 21, while on the early hours of Sunday morning (September 23), several Iveco lorries were targeted at a unit on Chasetown Industrial Estate.
Sergeant Richard Morris, from Lichfield Local Policing Team, said: “It appears that thieves are targeting vehicles at businesses and elsewhere to steal catalytic converters due to their scrap metal value.
“Anyone with information about these crimes should ring Staffordshire Police on 101, quoting incident number 328 of 23 September. Alternatively, they can ring Crimestoppers, anonymously, on 0800 555 111.”