Trading standards officials have launched an investigation into claims the county's garages are selling "contaminated" petrol.
Members of the public have complained some supermarkets and supermarkets in East Sussex have been sneaking ethanol into their fuels without telling customers.
Ian Hillier, a petroleum spokesman for the Trading Standards Institute, said: "It is illegal to do this and trading standards authorities in the affected areas have begun an inquiry.
"I understand that there have been around 75-100 complaints from people in south east England.
"Including ethanol in petrol is not really contaminating it, but there has be a clear warning to people who buy petrol as to exactly what is in it.
"Ethanol is actually seen as a green' measure but if it is sold without any warning then offenders are in breach of biofuel labelling regulations."
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