Hydrogen plays a crucial role in refining industry to meet the growing demand and stringent quality of produced gasoline and diesel. Steam methane reforming (SMR) is commonly used by refiners for on-purpose hydrogen production. However, despite being a mature and efficient technology, SMR has a considerable carbon emissions footprint that adds to the carbon intensity of petroleum fuels. Therefore, this paper examines utilizing Ontario province electricity grid that is based mostly on CO2-free sources of electric power to generate hydrogen by electrolysis using the concept of 'power-to-gas'. Consequently, the study evaluates the deployment of a series of 1 MW nameplate capacity polymer electrolyte membrane (PEM) electrolyzers to produce 25 MMscfd of hydrogen for a refinery, instead of the conventional pathway based on steam methane reforming. It assesses the production costs and life cycle emissions for five production scenarios to meet the hydrogen demand of the refinery. Aspen HYSYS and mixed integer linear programming models are employed for the purpose of this study. Steam methane reforming provides a lower cost hydrogen under low natural gas prices, even with stringent carbon-pricing policy. However, the renewable electrolytic hydrogen production method shows a potential to curb significant carbon emissions from steam methane reforming level, increasing the CO2 free energy and renewable content of the gasoline and design within the life cycle production scheme. This power-to-gas hydrogen production can be compared to eliminating as many as 34,893 gasoline passenger vehicles from the road. Accordingly, supplying electrolytic hydrogen to a refinery by a grid powered from clean energy sources is considered a good venue for providing decarbonization of petroleum fuels. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.