If you have the money, I highly recommend ExcelWriter by Soft Artisans. It is a multi-threaded COM object that you instance and pass parameters to and bang you get Excel output. No problems with instancing Excel as an object, no speed problems (ExcelWriter is fast C++), no size problems, nothing. Just great Excel output. I am not sure what you are doing with Excel, but if you are just doing output it is a great product. You can even put VBA, multiple worksheets, and charts in your output. And it is fast!