According to ARIN (American Registry of Internet Numbers), no more IPv4 addresses are available with them as of yesterday. This means their IPv4 pool is totally empty now.
It practically means that organizations that want more IPv4 IP addresses will have to either buy these IPv4 addresses from others who own these are are willing to sell. They cal also join the waitlist and wait till these become available with ARIN. And the third option is to use IPv6 IP addresses. The CEO of ARIN, John Curran, had said in an earlier interview that he does not expect that many new IPv4 addresses will become available with ARIN, therefore the chances for those on the waitlist are minimal.
According to an ARIN announcement the sale of IPv4 addresses can be made without any restrictions. Previously, they required that the organizations that sell their IP address could not get new addresses assigned from ARIN within twelve months of transferring their own IPv4 address to another organization. Trading in addresses work quite well for small requirements but larger ISPs might be required to pay millions of dollars to buy large blocks of these address.
The adoption rate for IPv6 has been quite fast but still only 21.31 percent users are IPv6 enabled in the US. It may be noted that more than 99.967 percent of IPv6 addresses are still available. However, in order to communicate on IPv6, both the end user and the server should be IPv6 enabled. Only 14 percent of the top US sites support IPv6. No immediate timetable is available for switching from IPv4 to IPv6 but it is bound to happen sometime in future.