Abstract The use of Autonomous Underwater Vehicles (AUV) is an emerging technology in many fields of marine activity (military, scientific, industrial), offering a significant potential in cost savings and extension of the operational capabilities related to the solutions currently adopted in offshore operations. Commercially available AUVs are mainly used by the oil & gas industry for the execution of seabed surveys and they are not routinely applied for carrying out the environmental monitoring and asset integrity around oil&gas offshore infrastructures. Eni e&p and its subsidiary Eni Norge, in cooperation with Tecnomare, have launched the CLEAN SEA project (Continuous Long-term Environmental and Asset iNtegrity monitoring at SEA) with the objective to use a commercially available AUV, properly upgraded with key enabling technologies, for the execution of environmental monitoring and asset integrity in offshore fields where eni operates. This paper will address how to reach this goal. A custom designed mission payload, arranged as modular and interchangeable pods, has been installed at the AUV. These modules, characterised by a set of sensors, are built to perform different offshore monitoring activities according to specific needs: automatic water samples collection; visual inspection (asset, seabed) and hydrocarbon leakage detection; automatic chemical analyses of trace pollutants and acoustic survey of seabed and pipelines / flowlines. This paper will in addition illustrate the possible future extension of the AUV operational capabilities through the integration and field demonstration of key technologies such as underwater docking, wireless underwater communication for mission data downloading and wireless power recharge for increased autonomy. This may enable a "permanent" operation subsea independently of support from surface. A comprehensive technical overview of the concept will be presented as well as the results of the demonstration tests.