Composite stacks were constructed by superimposing 6 to 13 benthic foraminiferal δ18O records covering the period 0--850 ka. An initial timescale for each core was established using radioisotopic age control points and assuming constant sedimentation rates between these points. The average of these records is our 13-core untuned stack. Next, we matched the 41 kyr component of each record individually to variations in Earth's obliquity. Four of the 13 records produced timescales that were inconsistent with one or more of the known radioisotopic ages. The nine remaining cores were averaged to create a minimally tuned stack. Six of the minimally tuned cores were assembled into a tropical stack. For each stack we estimated the uncertainty envelope from the standard deviation of the constituents. Spectral analysis of the three stacks indicates that benthic δ18O is dominated by a 100 kyr oscillation that has a narrow spectral peak. The contribution of precession to the total variance is small when compared to prior results from planktic stacks.