as of/as at

[Unregistered]

I would like to know whether "as of" and "as at" are synonimous in these phrases:
balance sheet as of 31 December 2006
balance sheet as at 31 December 2006.
What is the meaning of "as of" in this case: up to that date or on that date?
Thank you very much!

[Anglika]

They are synonymous in this context.