Oil is recycled from cooking waste to power diesel vehicles
Businesses have been warned by police to be on their guard against rogue traders collecting waste cooking oil.
A man pretending to be a legitimate carrier was cautioned under the Fraud Act earlier this week for targeting one Pembrokeshire tourist attraction.
There have also been reports of thieves stealing waste oil which can be turned into bio-diesel to power vehicles.
Commercial collectors must be licensed while businesses need to be able to prove how they dispose of their waste.
On Monday Dyfed-Powys Police issued a caution to a man who took four 20 litre cans of used cooking oil from Folly Farm, near Narberth.
Pc Keith Barclay, based at Narberth police station, said legitimate commercial collectors needed a waste carriers licence and had to issue waste transfer notices upon collection.
He said businesses needed to account for waste cooking oil and prove it had been disposed of correctly "down to the last drop".
"I'm sure the last thing they would want is to be caught out and face a fine," he added.
He said police were also aware of reports of waste oil put out for collection being stolen before it was picked up.
"There are people out there picking it up when they should not be - that's theft," he added.
Connla Wielding-Jones is a licensed waste oil collection driver for Ammanford-based Sundance Renewables, which processes used cooking oil into bio-diesel.
He collects from hotels, cafes, schools, chip shops and takeaways in west Wales and said sometimes batches put out for collection went missing before he arrived.
"It is quite common but I would also say it's opportunists, private individuals," he said.
"It was a waste product a couple of years ago, now some collectors are involved in a bidding war. It can be a bit cut-throat."
He said used oil could fetch up to a maximum of 20p a litre.
"It has got a value because it is an energy so there is competition - there are some big oil collectors about."