Abstract: A method of preparing high density fuels by the addition-rearrangement of pentacyclo[7. 5. 1. O.sup.2,8 . O.sup.3,7 . O.sup.10,14 ]pentadecane. The process comprises the steps of:(a) reacting pentacyclo[7. 5. 1. O.sup.2,8 . O.sup.3,7 . O.sup.10,14 ]pentadecane with an adequate amount of super acid and solvent under inert gas condition to obtain a solution and maintaining at a reaction temperature of 0.degree. C. to 200.degree. C. and a pressure of about 1.0 atmosphere to about 100 atmospheres for a period of from about 10 minutes to about 100 hours to obtain a solution;(b) stirring the solution for a suitable time to complete the addition-rearrangement reaction;(c) separating the reaction mixture in water to obtain an aqueous layer and an organic layer.(d) washing the organic layer with an alkali solution to eliminate any residual acid; and(e) purifying the organic layer by distillation to obtain the desired product.