Fifty-one are corporations, and General Motors comes in at number twenty-three, just ahead of Denmark (the data are from 2000, Wal-Mart should be higher than listed, among other changes).
To be sure, these comparisons are problematic. Yearly sales are not strictly comparable to gross domestic product. Furthermore countries “hold” human capital and other forms of wealth in ways that corporations do not. Read Eric Rasmusen on the immense wealth of the United States. So these measures underestimate the economic significance of nations relative to corporations. Still they offer an object lesson in the importance of effective culture and incentives. How should Bangladesh feel, 133 million people strong, with a yearly gdp smaller than the sales of Hewlett-Packard?
Addendum: Here is more detail on why the comparisons are misleading. In a nutshell, gdp figures are based on “value added.”