Looking at a test grid, the FZ18's lens exhibits what I like to think of as a distortion struggle; rather than an overall barrel distortion at its widest angle, there are small, shifted pockets of the grid (not shown). In practice, such as this shot here, you can see some slight distortion on the right side. (Grid added in Photoshop.) Overall, the FZ18's lens gets good marks for geometry, especially since its 28mm-equivalent wide angle would be expected to show more barrel distortion than it does.
Photo credit: Lori Grunin