I haven't tried water soluble oil paints yet because I haven't heard much good about them in terms of workability. However I came across this artist review of the Daniel Smith WSO's and now I may have to try them.
When I get this accomplished I will post the results with my experience. In the meantime, here's a video that talks a little more about these paints:
I often order through the online art supply sites, however, we are very fortunate here in the Northwest to have a Daniel Smith outlet store. They carry a huge product offering that you can feel and touch before buying. Of course you can purchase many brands at our other stores like Seattle Art, Dick Blick and Utrecht, but they don't carry Daniel Smith brand products. Dan Smith also has a catalog for ordering from longer distances.
So if this product is as good as they claim, I want to know about it. BTW, they have a 10% off promotion on these right now.