A full ink reservoir, that no ink drying will occur before "last use", and that the pen is of standard grade, and not some cheap chinese copy. In that case, I believe that some tests were run a few years ago by Bic as part of an advertising campaign. Assuming ball head wear is kept to a minimum, those pens were able to draw a line for two miles before the ink supply was exhausted. In average daily use, that could mean non-stop writing for several months, assuming each page of handwritten text is equal to approximately 50 feet of line (a rough estimate)
