CO₂ and/or H₂O were reduced to CO/H₂ in micro-tubular solid oxide electrolysers with yttria-stabilized zirconia (YSZ) electrolyte, Ni-YSZ cermet cathode and strontium(II)-doped lanthanum manganite (LSM) oxygen-evolving anode. At 822 °C, the kinetics of CO₂ reduction were slower (ca. −0.49 A cm−2 at 1.8 V) than H₂O reduction or co-reduction of CO₂ and H₂O, which were comparable (ca. −0.83 to −0.77 A cm−2 at 1.8 V). Performances were improved (−0.85 and −1.1 A cm−2 for CO₂ and H₂O electrolysis, respectively) by substituting the silver current collector with nickel and avoiding blockage of entrances to pores on the inner lumen of micro-tubes induced by silver paste applied previously to decrease contact losses. The change in current collector materials increased ohmic potential losses due to substituting the lower resistance Ag with Ni wire, but decreased electrode polarization losses by 80–93%. For co-electrolysis of CO₂ and H₂O, isotopically-labelled C¹⁸O₂ was used to try to distinguish between direct cathodic reduction of CO₂ and its Ni-catalysed chemical reaction with hydrogen from reduction of steam. Unfortunately, oxygen was exchanged between C¹⁸O₂ and H₂¹⁶O, enriching oxygen-18 in the steam and substituting oxygen-16 in the carbon dioxide, so the anode off-gas isotopic fractions were meaningless. This occurred even in alumina and YSZ tubes without the micro-tubular reactor, i.e. in the absence of Ni catalyst, though not in quartz tubes. Unfortunately, larger differences between the thermal expansion coefficients of quartz and YSZ precluded using a quartz tube to house the micro-tubular reactor. However, the kinetic results, CO/H₂ yields from off-gas analysis, diffusional considerations and model predictions of reactant and product gas adsorption on Ni suggested that syngas should be produced by electrochemical reduction of steam to H₂, followed by its Ni-catalysed chemical reaction with CO₂.