We develop an a priori error analysis of a finite element approximation to the elliptic advection-diffusion equation - epsilon Delta u + a . del u = f subject to a homogeneous Dirichlet boundary condition, based on the use of residual-free bubble functions. An optimal order error bound is derived in the so-called stability-norm [GRAPHICS] where h(T) denotes the diameter of element T in the subdivision of the computational domain.