Objectives:We propose to field a new instrument capable of real-time, in-situ, high-resolution measurement of dissolved gases and volatile organic compounds in the marine environment. The instrument is a membrane inlet mass spectrometer (MIMS) designed to operate either autonomously on a towed or moored platform or as an instrument package on board an autonomous underwater vehicle (AUV). The two-year objective is completion and successful underwater demonstration of a prototype instrument packaged in a pressure sphere compatible with freestanding use or as an Odyssey payload. Methodology:The proposed instrument will comprise: a vacuum system, a mass analyzer, and necessary electronics system. An inlet, exposed to the water column, is designed to exclude water while allowing for analyte gas inflow to the instrument. The ion pump and vacuum envelope maintain a low-pressure environment, permitting analyte ionization, mass analysis, and detection. Other electronic circuitry produces the various voltages required for analyte ionization and ion acceleration. Much of the design of individual components is competed, and the work will focus on construction, interconnection and mounting, and testing of system components within the pressure sphere. Rationale:The AUV/MMS will fill in an important, unmet need of oceanographic scientists as well as applied ocean technolgoists. Some specific examples of research and management/monitoring efforts that will benefit include: Investigations of methane seeps, and related offshore oil exploration, hydrologic research, monitoring of water quality unobtrusively from an AUV, or over time at a single location (e.g. in aquaculture settings); in basic ocean research, and in mapping of marine oil spills. The broad range of applicability of a successful MMS/AUV makes it relevant to several Sea Grant themes, including Marine Biotechnology (through improved sensors for chemical conditions), Coupled Ocean Observation and Modeling (through real-time chemical observation), and Coastal Management and Utilization (through ecological and pollution monitoring).