Sure. First, you'll need a full subscription to EF, not one of their freebie trial packages.

Then click on the "fare information" box, and when that screen appears, but the same airport code into the "Departing airport," "Arriving airport" and "Purchasing city" boxes. Put any "departing dare" you like in that box (but I usually enter a month or so from the present) and enter at least one Oneworld airline code in the appropriate box. I usually use AA or BA. Choose whatever currency you want the options to show (USD is the default) and press "Search."




You'll get the results screen that looks like this:



...on which you can see the base fares (before taxes and fees) for various Oneworld RTW products.

You will need to do this for each country from which you contemplate starting a RTW trip. You can get similar results for Star Alliance or Skyteam RTW products by inserting one of those alliances' airline codes in the "airlines" box, or reduce the length of the list by specifying which cabin (Y, J, F) you want to use, etc. Leaving the "airlines" boxes empty will cause the tool to put all results from all carriers, which can be quite lengthy. Note you can also click on the "rules" icon to see the various products' rules.

This can be a tedious exercise if you're looking for the cheapest (meaning what?) origin point. Remember that taxes, fees and "positioning" costs will be on top of the base fare.

Good luck!