Abstract: A monoport airgun for seismic exploration has a single discharge port extending continuously for 360.degree. around its longitudinal axis. This airgun has a first housing providing a firing chamber containing pressurized gaseous fluid (gas) and a second housing providing an operating chamber. The first and second housings are positioned in alignment along the longitudinal axis. They are spaced apart along this axis for defining the discharge port between them extending continuously around the axis. The two housings of the monoport airgun are interconnected solely by a guide member concentric with the axis. A shuttle encircling the guide member is movable therealong between closed and open positions. In closed position, the shuttle closes the firing chamber for retaining pressurized gas therein. In open position, the shuttle opens the firing chamber to the discharge port for allowing pressurized gas to blast from the firing chamber through the discharge port.