This is because "Oxford" could refer to a city, town, or region in many different countries, and each of these locations might have its own postal abbreviation.
To get the correct postal abbreviation, you need to specify the location you're referring to. For example:
* Oxford, England: No official abbreviation. You would simply use the full name "Oxford" in the address.
* Oxford, Mississippi, USA: The postal abbreviation is "MS".
* Oxford, Ohio, USA: The postal abbreviation is "OH".
Please provide more context so I can help you find the correct abbreviation!