I too wanted to export Outlook OST to PST from a long time, so I downloaded eSoftTools MBOX Converter Tool and tried it and indeed within a few minutes my Outlook OST file got exported to PST. It has many features available which are very pleasant to use. Apart from this, this software is user friendly which is also very pleasant to use. It also has a Free Demo available using which you can export 25 emails from OST to PST.
I myself have exported my Outlook OST to PST using eSoftTools OST to PST Converter Tool which has amazing features and exports OST file without losing any data.