In this paper, we present the results from first-principles study based on the electronic structure and adsorption characteristics of CH4, CO2, H-2 and NH3 adsorbed on Ca decorated/doped phosphorene. Our study finds that phosphorene exhibits n-type behaviour on decorating calcium, and p-type on doping calcium. Gas molecules are physisorbed on both pristine and calcium-mediated phosphorene, visible through their lower binding energy and charge transfer values. Ca decorated phosphorene is suitable for hydrogen storage due to its higher binding energy for H-2. Ca doped structures shows increased binding affinity towards CH4 and NH3 in zigzagl direction and armchair directions respectively. The extracts of our study implies that Ca doped phosphorene possess increased binding affinity towards gas molecules, and the results are highly helpful for gas adsorption and to design gas sensors based on calcium doped or decorated phosphorene. (C) 2016 Elsevier B.V. All rights reserved.