The following statistics are compiled by the Regional Internet Registries. Each ASCII text report contains summary reports of the allocations and assignments of numeric IP address space made by the respective RIR:
Global Internet Resources Distribution
The Number Resource Organization provides an Internet Number Resource Status Report, which is updated quarterly.
The results of an audit of IPv4 address space, jointly conducted by APNIC, ARIN, and RIPE NCC in July 2002, are also available here.