See this pdf for more information.
If you were asking about a two currency arbitrage between different markets. For example, the BTC/USD exchange rate at MtGox and one at Intersango then the following formulas apply considering brokerage fees at both exchanges.
For simplicity I am using BTC as the base currency and USD as the quote currency, but you can exchange these easily.
Assume:
A is the exchange rate of BTC/USD on exchange MtGox
B is the exchange rate of XXX/YYY on exchange Intersango
Fa is the fee of MtGox
Fb is the fee of Intersango
There is a no arbitrage opportunity if A = B + ( Fa + Fb )
But if A - B > Fa + Fb then the the base currency, BTC, is cheaper on exchange B than in A. So the person would buy BTC on Intersango (B) and sell BTC on MtGox (A).
profit = A - B - ( Fa + Fb )
If B - A > ( Fa + Fb ) then the base currency, BTC, is cheaper on exchange A than in B. So the person would buy the BTC on MtGox (A) and sell it on Intersango (B).
profit = B - A - ( Fa + Fb )
Other arbitrage opportunities will exist such as triangular arbitrage. But those won't develop until the exchanges not only have BTC/fiat currency pairs but other currency pairs as well.
1http://bitcoin-analytics.com/#arbitrage provides realtime arbitrage panel which supports history of arbitrage opportunites between all major markets. – Yevgen Martynov – 2013-08-16T14:34:42.800
1
See also http://bitcoin.stackexchange.com/questions/121/is-there-an-efficient-way-to-exploit-arbitrages-between-the-different-exchanges
– ripper234 – 2011-09-04T23:09:27.7701This seems like a very time dependent question, doesn't it? – D.H. - bitcoin.se – 2011-09-05T05:25:45.383
1@D.H. - True, but check out the answers, they contain important timeless information and links. – ripper234 – 2011-09-05T07:45:04.283
1Could we at least change the title then? If the answer contains timeless information I'm sure we can make the question more timeless. Perhaps something like: "How can I exploit possible arbitrage opportunities in Bitcoin markets?" – D.H. - bitcoin.se – 2011-09-05T16:58:26.000
@D.H. Edited, but not to the title you suggested. – ripper234 – 2011-09-05T19:56:32.930
Good, that's much better. – D.H. - bitcoin.se – 2011-09-05T20:24:05.223