Photoshop JPEG Quality

I use Photoshop 7, admittedly somewhat outdated, but it serves my needs. When I open an existing image and then 'Save As' a new filename, it gives me an image quality choice ranging from 0 to 12. I've found that 10 or 11 saves the image in approximately the same file size as the original, while 12 saves it in a much larger file size. Does this mean that 12 might save it with no quality loss from the original? If not, why would the new file size be significantly larger than the original?