THE penalty for selling or buying illegal diesel is to rise by five times. People who supply or buy marked or detreated diesel oil for vehicle use could be fined up to $1 million and jailed for two years under an amendment to be gazetted on Friday. Marked oil is a red-coloured diesel which is produced for industrial use and is exempt from duty. Detreated oil is marked oil without the colouring substance. In a paper to legislators, the Finance Bureau said diesel sold on the black market had become a serious problem. It had led to revenue loss, environmental pollution and fire hazards. Officials have said nearly $2 billion in duty on light diesel was lost last year. But officers had had problems differentiating illegal and duty-paid fuel. The bureau said the only difference was their sulphur content. Detreated oil or fuel illegally imported from China has a sulphur content higher than the regulation 0.05 per cent by weight. The Government plans to launch more large-scale operations against illicit fuel. Since September, authorities have arrested 21 people and seized 20,361 litres of illegally imported fuel, 6,035 litres of marked oil and 15,098 litres of detreated oil. The Customs and Excise Department has said it will review the rewards it pays informers and plans to tighten controls on exporting oil, to try to prevent oil from being illegally shipped back to Hong Kong. Export permits will only be issued when exporters produce documentation.