It depends. Is the file 10MB because it truly contains 10MB of data (this would correspond to roughly 100,000 cells of numbers)? Or is it 10MB because of "bloat" resulting from the usedrange problem?
If you are not familiar with the usedrange problem, there is a UsedRange property for each worksheet. This is the range of cells that Excel saves when the workbook is saved. It is supposed to the the smallest rectangular block of cells that contains every cell that has been changed--containing either data, formatting, validation, comments, etc. But there is a problem with Excel that it does not always collapse the usedrange properly when data are deleted from a worksheet. So Excel saves cells that don't need to be included in the file, and this increases the file size. You can check whether you have a problem by selecting any cell on a worksheet and typing Ctrl-end (using the end keyboard key). The selection will then go to the last cell (lower right corner) of the usedrange. If this cell is outside the range of the sheet containing data then you have usedrange bloat. There are numberous posts on this board regarding this problem and how to clean it up.
If you truly have 10MB of data your only option is to figure out a way to store less of it. I should mention that 100,000 cells of number sounds like a lot, but this is the number of cells in the range A1:CV1000 in one worksheet.
That was a great read Damon and thanks for that. pkohli... I've noticed a file size reduction by Zipping a file, opening it, and then saving it again. Seems like the Zip sheds some extra stuff? Anyways, I'm sure Damon's route is the way to go but you might want to trial something simple first. HTH. Dave