Mostly, yes. These painting are usually more expensive because the artist themselves have to spend a lot of money to paint with oil paint. Not only that, but oil is a rather difficult to become proficient with and so the artists has to be more skilled to use oil paint.
Why are oil paints more expensive?
The pigments of oil paint make it more expensive. Pigments are hard to produce, so that causes an increase in the price. Fun fact: A good quality oil paint tends to have 75% pigment.