There is another thing to consider. Using surrogate keys could cause you application to need more joins Thus negating you 15 millisecond performance gain. I think that the real answer depends on what type of data you are trying to store. Whether or not to use varchar2's or numbers depends on a number of factors. There are situations where Varchar2's would be preferable and there are situations where they would not be preferable. One other consideration is that if you are using a true surrogate key then the value of the key is probably derived from a sequence. Fetching the sequence might take a few milliseconds thus throwing off your numbers.