The Cygnus 3D Marine Seismic Survey (MSS) is a three-dimensional marine seismic survey in Commonwealth waters of the Vulcan Sub-basin. Phase 1 and Phase 2 of the Cygnus 3D MSS were previously completed between December 2015 and March 2016 in accordance with environmental management measures detailed in a previously accepted Environment Plan (NOPSEMA reference 3446), which is valid until the 31st December 2017. This revision of Environment Plan is submitted to NOPSEMA to allow for an extension to the timeframe of the Cygnus 3D MSS EP to the 31st December 2018. The original Cygnus 3D MSS EP Survey Area has also been refined to include a smaller Operational Area and Acquisition Area for Phase 3 of the Cygnus 3D MSS. The Acquisition Area comprises the area within which 3D seismic acquisition will be undertaken and covers approximately 7,240 km². The Acquisition Area is surrounded by a larger Operational Area, which comprises additional area for the purpose of line turns, run-ins, run-outs, soft starts, source testing, etc. The Operational Area is located approximately 170 km off the Kimberley coast of northern Western Australia (WA) and 180 km from the Indonesian archipelago and East Timor. The survey will be undertaken in Commonwealth waters in water depths of up to approximately 245 m.Phase 3 of the Cygnus 3D MSS is expected to comprise the following:• Phase 3 North;• Phase 3 South; and• Potential additional orthogonal infill lines within the Phase 1 area.The next phases of the Cygnus 3D MSS are anticipated to take a total of approximately 2 – 3 months to acquire, completed between 2017 and 31st December 2018.