In our laboratory, methane conversion to higher hydrocarbons in "one-srep" process under non-oxidative condition at low temperature was first introduced and investigated over Pd-Co/SiO2 prepared by sol/gel method [Guczi et al., Catal. Lett. 54 (1998) 33] and over Pt-Co/NaY [Guczi et al., Stud. Surf. Sci. Catal. 119 (1998) 295] bimetallic catalysts. It was found that methane conversion in one-step process is at least 2.5 times higher than that measured in "two-step" process on the same catalysts. In the present work, the two-step and one-step processes are compared. It has been established that in one-step process when methane dissociation occurs in the presence of hydrogen containing helium, not only the production of higher hydrocarbons increases but also the selectivity is shifted towards larger molecules. Palladium-cobalt system proved to be more efficient than the corresponding platinum-cobalt catalysts. (C) 2001 Elsevier Science B.V. All rights reserved.