We report experimental results on an efficient singly resonant optical parametric oscillator (OPO) based on periodically poled MgO-doped LiNbO3. The OPO was pumped by a diode-pumped passively Q-switched Nd:GdVO4 laser, which could produce 3-ns laser pulses with a repetition rate of 5 kHz. By changing the crystal temperature and grating periods, the OPO generated signal and idler output in the ranges of 1.41 to 1.78 µm and 2.7 to 4.3 µm, respectively. The maximum output power at the signal wavelength of 1.55 µm was 35.4 mW with 120-mW pump power. The possibility of using the OPO for trace gas detection was demonstrated through measuring the absorption spectra of methane.