Sustainable development of separate regions and countries is affected by array of factors among which energy security plays a cricial role. We claim, that efficient use of energy is very important constutuent of energy security. The first part of the presented paper we wil devote to overview of perception of energy security and revealing waht role energy efficiency plays. Energy efficiency could be estimated by energy intensity indicator, which shows what ammount of energy is used for e.g. one European Euro. This indicator can be calculated for main sectors of economy: various branches of industry, services and agriculture. The higher value added is created in the sector, or, to put it in onother way, the higher activity of sector, the more important that energy in this sector would be used efficiently. In this paper we tackle longterm activity and energy efficiency of agriculture sector in developed and less developed countries.We raise an assumtion that in better developed countries activity of agricultural sector in long-run would diminish, what would be followed by gradular increase in energy intensity; i.e. energy intensity indicator would gradually diminish. Besides, we assume that those tendencies would be slightly different in currently less developed countries; i.e. agricultural sector not necessarely would contract and energy intensity would diminish with higher rates if to juxatopse with better developed countries. In order to verify raised assumptions data of the selected European countries will be used. Better developed countries would be represented by one country – Germany. Less developed European countries would be represented by Bulgaria and Romania. We will forecast activity and energy intensity by using LEAP software. Indicated data for chosen countries will be forecated untill year 2050. Obtained results will indicate if consitent patterns could be traced and respective policy implications formulated.