See "2. Reading a file" in How To : Read and Write Office 2003 Excel XML Files | Odie's Oracle Blog
You can use the external table (or SQL*Loader) to bulk load all files at once in a binary XMLType table, and then using XMLTable to query the content.
There's another way I've been exploring recently, involving the external table preprocessor and XSLT, but it only performs well in the latest 12.1 release.
You can read more here if interested : XMLTABLE vs. External XSLT preprocessor | Odie's Oracle Blog
But for your current requirement, an XMLTable query as described in the first link should be just fine.