  SuperWASP light curves for 53 W UMa-type eclipsing binary (EB) candidates,
identified in previous work as being close to the contact binary short-period
limit, were studied for evidence of period change. The orbital periods of most
of the stars were confirmed, and period decrease, significant at more than 5
sigma, was observed in three objects: 1SWASP J174310.98+432709.6 (-0.055
\pm0.003 s/yr), 1SWASP J133105.91+121538.0 (-0.075 \pm0.013 s/yr) and 1SWASP
J234401.81-212229.1 (-0.313 \pm0.019 s/yr). The magnitudes of the observed
period changes cannot be explained by magnetic braking or gravitational
radiation effects, and are most likely primarily due to unstable mass transfer
from primary to secondary components, possibly accompanied by unstable mass and
angular momentum loss from the systems. If these period decreases persist, the
systems could merge on a relatively short timescale.
