Industrial microwave tunnel ovens have previously been analyzed using the finite difference time domain (FDTD) method. However, it has been observed that since the computation time on normal computers often becomes very long, it is desirable to develop more efficient methods. In this paper an approach based on the moment method (MM) is used to calculate the electromagnetic field in a tunnel oven. The oven consists of a rectangular cavity mounted on a flat tunnel, containing one or more dielectric layers. The layers correspond to e.g. the food load and the conveyor belt. It is shown that the results from the MM calculations agree well with the FDTD method and that the computation time, compared to FDTD, is significantly reduced. For some problems, the computations are sped-up by a factor of 100. By combining the fast MM computations with the simulated annealing method for optimization, together with suitably chosen performance criteria, it is shown how the design process can be drastically shortened. By varying the dimensions of the cavity and the tunnel, the power distribution in the loads can be optimized for a wide range of applications,and, since the basic design of the ovens is kept constant, the development cost for new equipment can be reduced.