A narrow-linewidth MgO:PPLN optical parametric oscillator (OPO) with two volume-Bragg-grating (VBG) mirrors in a linear cavity configuration is presented. The OPO was pumped at 1064 nm, generating an idler wave near 2.5 . The OPO performance in the two-VBG-mirror cavity is compared with its performance in other mirror combinations. Nearly 0.5-W output in a single longitudinal mode was obtained. The narrowest linewidth of 2 GHz was obtained when the two VBG mirrors were slightly detuned from one another.