TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The additive further comprises other additives. The additive further comprises alkenes (less than 25%, preferably less than 10%). Preferred Components: The fuel additive is present at more 10 than 3 (preferably more than 90)%. The organic compounds have a molecular weight of more than 100 (preferably less than 800) Dalton. The organic compounds consist of hydrogen and carbon atoms. The ring structures are saturated with hydrogen atoms. Either at least one ring structure comprises a side chain of hydrocarbon (optionally saturated) or all the ring structures comprise a side chain of hydrocarbon (optionally saturated). The amount of the cyclic organic compound is more than 3 (preferably more than 80)%. The flash point is at least 100 degrees C. The content of molecules containing ring structures which share at least one atom is less than 1%. The additive comprises a mixture of compounds having 2-4 rings, where the linker between the rings is a propylene group, without any side chains and where the end rings should have alkyl chains of 5-12C in the para position. The fuel has a density of 760-850 kg/m3.    TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The polymerization is conducted at more than 150 degrees C, preferably less than 400 degrees C, and at a pressure of more than 35 (preferably less than 65) bar. The hydrogenation is conducted at more than 350 degrees C, preferably less than 600 degrees C, and at a pressure of more than 35 (preferably less than 65) bar. The formed polymers are separated via distillation, chromatography or any other suitable technique. A lubricant is added to the hydrogenated polymers. EXAMPLE - Hydrogen gas and carbon monoxide mixture in molar ratio of 1 to 1.7 was contacted with iron Fischer-Tropsch-catalyst, at 230?OC. The 2-6C olefins (alkenes) (products of the Fischer-Tropsch synthesis) were separated using zeolite adsorbent to give alpha-olefins (1-alkenes). The mixture comprising 2-6C 1-alkenes was polymerized in a lab reactor. The alkenes were fed at 1kg/hour for 8 hours. Then zeolite-based polymerization catalyst (COD 900) (0.7 l) was added and the polymerization was conducted at 300 degrees C and at 50 bars. The polymerized product was hydrogenated in a lab reactor using hydrogenation catalyst (TK-553), at 450 degrees C and at maximum pressure of 50 bars. Then lubricating additive (LA 99 C) (500 ppm wt) was added to give fuel.