Resize your browser window and watch how it affects the behaviour of each table. Notice the only table that does not expand or collapse to accommodate the window dimensions is the one that uses absolute cell widths and an invisible GIF in each cell.

Table with no cell widths

No width specifiedNo width specified

Table with relative cell widths

Width = 30%Width = 70%

Table with absolute cell widths

Width = 100Width = 250

Table with absolute cell widths and single-pixel GIF

Width = 100

Width = 250