Integrated liquid fuel catalytic partial oxidation (CPOX) reformer and fuel cell systems can include a plurality or an array of spaced-apart CPOX reactor units, each reactor unit including an elongated tube having a gas-permeable wall with internal and external surfaces. The wall encloses an unobstructed gaseous flow passageway. At least a portion of the wall has CPOX catalyst disposed therein and/or comprising its structure. The catalyst-containing wall structure and open gaseous flow passageway enclosed thereby define a gaseous phase CPOX reaction zone, the catalyst-containing wall section being gas-permeable to allow gaseous CPOX reaction mixture to diffuse therein and hydrogen rich product reformate to diffuse therefrom. The liquid fuel CPOX reformer also can include a vaporizer, one or more igniters, and a source of liquid reformable fuel. The hydrogen-rich reformate can be converted to electricity within a fuel cell unit integrated with the CPOX reactor unit.