We investigate the statistics of gravitational lenses in flat , low-density cosmological models with different cosmic equations of state \omega .
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 \omega > -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 \omega .
The wide-separation ( \theta \gtrsim 4 ^ { \prime \prime } ) lensing rate is a particularly sensitive probe of both \omega and the halo mass concentration .
The absence of these systems in the current JVAS/CLASS data excludes highly concentrated halos in \omega \lesssim - 0.7 models .
The constraints can be improved by ongoing and future lensing surveys of > 10 ^ { 5 } sources .