Due to its compactness, high heat and mass transfer rate and ease of manufacture, coiled/spiral tube has been widely used in process industries, especially as heat exchangers and chemical reactors. This study addresses the mass-transport enhancement and reaction performance in in-plane spiral reactor with various cross sections geometries, i.e. circular, half-circular, rectangular, square, trapezoidal and triangular, at fixed cross-section area at several Reynolds numbers. The mass transfer performance is compared with those of straight channel counterpart. Laminar flow of gas with catalytic reactions is investigated using a validated three-dimensional computational fluid dynamics (CFD) model. The results suggest that spiral ducts offer better reaction performance as compared to straight duct, especially at higher Reynolds number. However, it imposes higher pressure drop. Amongst various cross-section, the coil reactor with half-circular geometry yields the highest reaction performance. This study can provide insight for design guidelines of high performance coiled reactor. (C) 2014 Elsevier B.V. All rights reserved.