This is quite regular techniques for artists since many centuries to do painting on wood panels or any canvas. Oil painting is a traditional method of creating a new painting with elements by using dry oil as base to stick paint over canvas. This technique is believed to be invented from Europe and than gradually used in all over the world. Main benefits of using oil painting is it's images are quite flexible and also color view is quite rich and also provides huge color range from light to dark. The disadvantage is this process is very slow. Once you do one layer, you have to give some time to dry it before you create another layer.
It it believed that first oil paintings was created in 7th century AD by one artist in Afghanistan. European people were used to make statues by using similar kind of methods and history says they are using it since 12th century mid. There are different methods of yellowing or drying paintings and different oils like poppy seeds, sunflower oil, linseed oil, walnut oil etc are used as per wide range of painting. As per requirements of patters and designs, artist may use different kind of oils. In single painting, artist may use different oils as per their requirements.