Carbamate synthesis has been studied over NaI-Pd/C in slurry, gas-solid, and tubular reactors at 373-438 K and 0.41-7.61 MPa. The gas-solid carbamate synthesis process in which the CO, O-2, methanol, and aniline reactants are present in the gas phase and the catalyst is in solid form occurs at a significantly higher rate than the slurry-phase synthesis in which CO and O-2 dissolve in the liquid methanol/aniline mixture. The high rate of the gas-solid carbamate synthesis compared with that of the slurry-phase synthesis can be attributed to (i) the intimate contact between the NaI promoter and the Pd on the carbon surface, (ii) the absence of solubility limitations in the gas-solid synthesis, and (iii) the slowing of the sintering of the Pd particles. Reaction pathway studies show that the direct oxidative carbonylation of aniline with methanol is the most effective pathway for carbamate synthesis. A low-cost, environmentally benign carbamate synthesis for the replacement of the isocyanate synthesis from phosgene/amine can be developed by coupling the high rate of the gas-solid synthesis with its intrinsic advantage of ease of catalyst recovery.