I would recommend to use an intermediate format like shapefile. First export your tables (Including table structure and data) from the PostGIS using "PostGIS SHapefile Import/Export Manager" which is installed with postgis.
There are some tools to import shapefiles into oracle DB. The one I suggest here is the Georaptor which you can install it as a plugin in Oracle SQL Developer. Georaptor is opensource (free) and easy to use. You can download it from here: