Decrease in oil prices and higher policy requirements focused on limitation of GHG emissions generated by fossil fuel plants, has an effect on national targets in energy production and distribution in Estonia. There are still debates regarding future energy trends in Estonia. On one hand, the historic dependency on oil shale as well as local origin of the resource, has stimulated the development of oil shale processing industries in the country. On the other hand, high demand and consumption of oil shale regularly raise the debate regarding the climate and environmental aspects of oil shale use. Political decisions on the decarbonisation of Estonia's oil shale sector requires a robust and scientifically justified platform for decision making. Besides, selection of decarbonisation alternatives will differ in accordance with the particular jurisdiction of stakeholders involved in the decision making process. Another set of aspects characterising the decision relate to involved trade-off, i.e. capital and O&M costs of clean energy technologies, sustainability and energy security of fuels used, direct and indirect CO2 emissions. A proper political decision on decarbonisation of the energy sector can provide opportunities for improved employment possibilities, creation of a new market niche and increase of business start-ups, a platform for industrial symbiosis or perspectives in order to reform the national economy towards a circular economy. The current paper defines four scenarios of decarbonisation of Estonia's oil shale industry. The present paper is focused on the definition of a methodological approach and sustainability categories for decarbonisation of the oil shale processing industry.