The list is not comprehensive, but includes metros from many major world cities. Mexico City's system comes in as the cheapest fare, while New York City's recently raised fare comes in around the middle of the list.
"New York's is also the only subway to run 24 hours a day, 365 days a year.
And in comparison to the fares of other subway systems in the "developed" world, New York's falls near the middle (that's not as good as free, as labor arbitrator Ted Kheel has demanded for decades, but hey). London, predictably enough, is the most expensive subway system by far."