steel chairs
You can use any kind of 10w-40 oil for a nighthawk
Baby oil
Most use Synthetic Oil.
If you are going to paint you should first find out what kind of paint was origanlly used on the chairs. Latex paint over oil based paint has been known to peel and come off. I think latex is the better choice because it does not yellow or fade over time. This website outlines the pros and cons of latex and oil paints: http://www.hgtv.com/decorating/painting-101-oil-or-latex/index.html You should use exterior latex paint on your adirondack chairs. Exterior latex will allow outside moisture to evaporate, which will prevent blistering/peeling of the paint.
Rocket oil
They use the oil God gave them in their oil glands.
synthetic oil
What are you substituting the oil with? What kind of recipe? You couldn't use butter for the oil in salad dressing. Sometimes it does matter what kind of shortening you use.
fully synthetic oil
Olive oil.
engine oil