Extended studies on Zn-ZSM-5 catalyst for the production of liquid hydrocarbons in the direct partial oxidation (DPO) of CH4 with O2 are reported. Previously, it was reported that metal-containing ZSM-5 catalysts could produce C5+ hydrocarbons from pure CH4/O2 feeds without feed additives. Zn-ZSM-5 produced the highest C5+ yields of the catalysts tested. This work shows that the method of introducing Zn onto the catalyst, ion-exchange versus impregnation, does not significantly alter C5+ yields if low Zn content is maintained (approximately 0.4-0.5 wt%). Liquid hydrocarbon yields in this system doubled after 8 h on stream while overall C2+ yields increased by over 300%. Mechanistic implications of these findings are discussed. Finally, processing a natural gas feed over Zn-ZSM-5 gave higher C5+ yields over CH4 feed but these yields were not improved over previously published results using HZSM-5.