  We investigate the statistics of gravitational lenses in flat, low-density
cosmological models with different cosmic equations of state w. We compute the
lensing probabilities as a function of image separation \theta using a lens
population described by the mass function of Jenkins et al. and modeled as
singular isothermal spheres on galactic scales and as Navarro, Frenk & White
halos on cluster scales. It is found that COBE-normalized models with w > - 0.4
produce too few arcsecond-scale lenses in comparison with the JVAS/CLASS radio
survey, a result that is consistent with other observational constraints on w.
The wide-separation (\theta > 4'') lensing rate is a particularly sensitive
probe of both w and the halo mass concentration. The absence of these systems
in the current JVAS/CLASS data excludes highly concentrated halos in w < -0.7
models. The constraints can be improved by ongoing and future lensing surveys
of > 10^5 sources.
