We report results from a systematic investigation of the effect of the temperature on the wettability of oil/brine/rock systems. An oil sample, produced from a sandstone reservoir, was tested on sandstone-like substrates (i.e., mica and quartz) in NaCl and MgCl2 solutions with concentrations ranging from 0 to 3 M. Raising the temperature from 25 to 50 degrees C has no discernible effect on the contact angle, regardless of substrate type, brine type, or salt concentration. Another oil sample, obtained from a carbonate reservoir, was examined on carbonate-like substrates (i.e., calcite) in NaC1 and MgCl2 solutions over a concentration range of 0-1 M. The contact angles decrease as the temperature increases from 25 to 65 degrees C, and this temperature effect also strongly depends upon the brine type and salt concentration. A systematic examination of the zeta potential of rock/brine and oil/brine interfaces under different conditions and subsequent discussions indicate that contact angle and zeta potential may not be directly linked. These findings regarding the wettability of oil/brine/rock systems may improve the understanding of low salinity wateflooding mechanisms by elucidating the combined effects of the temperature and other critical variables, including brine type, brine concentration, crude oil composition, and substrate type.