The relationship between injected wastewater produced during oil exploitation and triggered seismicity in Val d'Agri (Southern Italy) is investigated by using the Schuster’s spectrum of the seismicity and the singular spectrum analysis (SSA) of the volume and pressure time series of the wastewater. Our results suggest that most of the cycles found by using the Schuster’s spectrum of the earthquakes have periods very close to those identified in the SSA components of the volume and pressure of the injected wastewater. This could indicate that volume and pressure of the injected wastewater could be able to induce oscillatory variations in the seismic rate, and thus, to trigger earthquakes.