Concern has been expressed over a spate of oil thefts from commercial companies in Worcestershire.
Last week, a company in Worcester was left with a major clean-up operation after the theft from its premises.
The Environment Agency said a separate incident in Stourport-on-Severn could have caused serious pollution.
The agency says new regulations over storing oil at commercial premises will make it harder for thieves to get hold of fuel.
The Control of Pollution (Oil Storage) Regulations, which comes into force in September, will require companies to make their oil storage more secure and also provide a higher level of pollution protection.
Michael Morris, from the Environment Agency, said the thefts in Worcestershire had caused large spillages of oil.
“In one of these incidents oil entered drains.
“The company involved had to spend a considerable amount of money using specialist contractors to clean out the drains to prevent the oil getting washed into the nearby River Severn.”
West Mercia Police have also issued a warning to businesses to tighten security to prevent environmental damage.
A police spokesperson said: “Fuel thieves are not and never will be concerned with the actual, or potential, environmental damage involved in their crimes.
“We would, therefore, urge all individuals and organisations who store diesel oil, whether at domestic or business premises, to re-examine their individual levels of security and act accordingly now and not wait until the new regulations come into force in September.”