  For a singularly perturbed elliptic model problem with two small parameters,
we analyze finite element methods of any order on a Bakhvalov-type mesh. For
convergence analysis, we construct a new interpolation by using the
characteristics of layers. Besides, a more subtle analysis of the mesh scale
near the exponential layer is carried out. Based on the interpolation and new
analysis of the mesh scale, we prove the optimal convergence order.
