  Given that mergers are often invoked to explain many exotic phenomena in
massive star evolution, understanding the evolutionary phase directly preceding
a merger, the overcontact phase, is of crucial importance. Despite its
importance, large uncertainties exist in our understanding of the evolution of
massive overcontact binaries. We aim to provide robust observational
constraints on the future dynamical evolution of massive overcontact systems by
measuring the rate at which the periods change for a sample of six such
objects. Furthermore, we aim to investigate whether the periods of unequal mass
systems show higher rates of change than their equal mass counterparts as
theoretical models predict. Using archival photometric data from various
ground- and space-based missions covering up to ~40 years, we measure the
periods of each system over several smaller time spans. We then fit a linear
regression through the measured periods to determine the rate at which the
period is changing over the entire data set. We find that all of the stars in
our sample have very small period changes and that there does not seem to be a
correlation with the mass ratio. This implies that the orbital periods for
these systems are stable on the nuclear timescale, and that the unequal mass
systems may not equalize as expected. When comparing our results with
population synthesis distributions, we find large discrepancies between the
expected mass ratios and period stabilities. We find that these discrepancies
can be mitigated to a degree by removing systems with shorter initial periods,
suggesting that the observed sample of overcontact systems may originate from
binary systems with longer initial orbital periods.
