I'm not sure about Amazon in particular, but generally companies (especially tech companies) hold some percentage of stock in reserve for employee compensation.

I'm not sure about Amazon in particular, but generally companies (especially tech companies) hold some percentage of stock in reserve for employee compensation. However, the company can also buy back stock on the open market either to take it out of circulation (and thus increase the value of outstanding shares) or use it for employee compensation. Finally, if the board (as a proxy for individual owners) permits it, a company can issue new shares for any purpose including selling to raise cash for operations, or giving to employees as compensation. This isn't free money, however. New shares tend to dilute the value of existing shares. So owners often prefer to raise money other ways, like debt that doesn't convert to an ownership claim in the way stock does.