  In this paper, observational constraints on the cosmic equation of state of
dark energy ($p = w \rho$) have been investigated using gravitational lensing
statistics. A likelihood analysis of the lens surveys has been carried out to
constrain the cosmological parameters $\Omega_{m}$ and $w$. Constraints on
$\Omega_{m}$ and $w$ are obtained in three different models of galaxy
evolution: no evolution model (comoving number density of galaxies remain
constant), Volmerange and Guiderdoni model and fast merging model. The last two
models consider the number evolution of galaxies in addition to the luminosity
evolution. The likelihood analysis shows that for the no-evolution case $w \leq
-0.04$ and $\Omega_{m}\leq 0.90$ at $1\sigma$ (68% confidence level). Similarly
for the Volmerange $&$ Guiderdoni Model the constraints are $w \leq -0.04$ and
$\Omega_{m} \leq 0.91$ at $1 \sigma$. In fast merging model the constraint
become weaker and it allows almost the entire range of parameters. For the case
of constant $\Lambda$ ($w =-1$), all the models permit $\Omega_{m} = 0.3$ with
68% CL which is consistent with the value of $\Omega_{m} $ inferred from
various other cosmological observations.
