From numerical and analytical solutions of the normal mode equation for drift waves in a sheared magnetic field, the critical shearS cfor the onset of instability and the normal mode growth rates at subcritical shear are obtained. At low beta and without a parallel current it is shown that approximately twice the previously indicated shear is required for stability and the(m e / m i)1/3scaling ofS cis confirmed. The addition of a parallel plasma current is shown to increase initially the critical shear quadratically with current and then linearly at larger currents. The effect of electron and ion temperature gradients is studied with equal density and temperature gradients resulting in aproximately a 50% reduction inS c. Finally, the effect of finite beta on the critical shear is studied.