Oscillation criteria for second order neutral differential equations

Some oscillation criteria are given for the second order neutral delay differential equation [a(t)(x(t) + p(t)x(t - tau))']' + q(t)(x(t - sigma)) = 0, where tau and sigma are nonnegative constants, a, p, q is an element of C([t(0), infinity); R) and f is an element of C(R;R). These results generalize and improve some known results about both neutral and delay differential equations.