Marine diesel engines have long been subject to classification society rules. However, from the start of next year, a whole new - and quite separate control regime will begin to take effect with major implications for both new and existing engines. Annex VI of MARPOL 73/78, dealing with a wide range of air pollution control matters (including ozone depleting substances, acid deposition materials, volatile organic compounds, incineration and oil fuel quality), is still some way from reaching the required level of ratification to enter into force. Nevertheless, the time is fast approaching when some of the provisions of that Annex will start to take effect. This is particularly true in terms of the oxides of nitrogen (NOx) controls, Regulation 13.