Using fibre sensor networks, distributed information can be gathered even from places that are difficult or even impossible to be reached by other means. However, so far, such distributed fibre sensing networks are not capable of providing access to distributed chemical information along the fibre. In particular, highly selective and sensitive information on the concentration of various gases along the fibre cannot be obtained on a routine basis despite being desirable and needed in many different application scenarios. It is therefore tempting to explore the potential of integrating innovative optical gas sensing nodes along optical fibres, towards their massive deployment in existing telecom infrastructures. New developments in optical gas spectroscopy have opened up new prospects for remote gas sensing applications, addressing the limitations of current analytical methods in terms of sensitivity, ease-of-use and miniaturization. Nevertheless, there are important challenges to overcome before such a joint use of the fibers network for both communication and gas sensing becomes possible. GASPOF addresses these challenges, contributing to the development of the optical infrastructure of the future, where the communications network also acts as a large-scale distributed multi-parameter sensor. Focus will be put on two different optical techniques for gas sensing using the fiber-optics network: laser-based PTS and LHR. Both techniques will be advanced and integrated with the existing optical fibers network infrastructure. In parallel, we will investigate the possibility of using coherent OTDR for distributed gas sensing, while a reduced-cost approach for acoustic sensing will also be designed for measuring physical parameters of interest (e.g. vibrations) in addition to gas sensing. The GASPOF system configurations will demonstrate their performance and capabilities in important 4 application use cases.