Impact experiments for CO and H2 mixtures showed that hydrocarbon gases up to C4H10 are synthesized by shock. The conversion of Co to hydrocarbons increases with increasing shock energy but the composition of synthesized hydrocarbons depends on that of the reactant (H2/CO). From the results, geneses of some light hydrocarbons in planetary materials were inspected: Hydrocarbon gases contained in regoliths on the Moon's surface and in atmospheres of Jovian planets might have been produced by shocks that were caused by frequent meteorite falls and condensation-accretion of primitive solar nebulae into planets, respectively. Besides Fischer Tropsch reaction, impact-derived shock syntheses must have played an important role in the chemical evolution of astrophysical materials. ¿ American Geophysical Union 1994