For my trip to Oregon, I bought a selection of Holbein Duo water-soluble oils so I wouldn't have to deal with finding some thinner and oil mediums.  I've never used these before, but a number of my painting friends like them.  They do handle differently and take some getting used-to.  To try them out, I dashed off a couple very fast and loose sketches.  This is the consummate Oregon landscape--thick woods with a bare slope of clearcut.