Currently, Power-to-Gas technologies are considered viable solutions to face the onset problems associated with renewable capacity firming. Indeed, carbon-free hydrogen production converting renewable electricity excess and its injection into natural gas pipelines is considered a short-to medium-term solution. In this way, the so-called H(2)NG blends can be fired within internal combustion engines and micro gas turbines operating in CHP mode, offering better environmental-energy performances in machines. As regards the distributed energy generation scenario, the local H-2 production by means of electrolysis for methane enrichment will be more cost-effective if the oxygen is fruitfully used instead of venting it out like a by-product, as usually occurs. This study focuses on the usefulness of using that oxygen to enrich the air-fuel mixture of an internal combustion engine for micro-CHP applications, once it has been fuelled with H2NG blends. Thus, the main aim of this paper is to provide a set of values for benchmarking, in which H(2)NG blends, ranging in 0%-15% vol., burn within an ICE in partial oxy-fuel conditions. In particular, a preliminary energy analysis was carried out based on experimental data, reporting the engine operating parameters, gains and losses in both electrical and heat recovery efficiency. The oxygen content in the air varies up to 22% vol. A Volkswagen Blue Tender CHP commercial version (19.8 kW(el) of rated electrical power output) was considered as the reference machine and its energy characterization was reported when it operated under those unconventional conditions. (C) 2016 The Authors. Published by Elsevier Ltd.