It depends on who painted it.
If I painted it it would cost $50.
If it was painted by Picasso it would cost about $ 100 million.
The Starry Night is an oil-on-canvas painting by Vincent van Gogh.
The painting is oil on canvas and measures 100 x 70 cm. The painting is oil on canvas and measures 100 x 70 cm.
It is an oil painting on canvas.
Oil on canvas
Oil on canvas
It is an oil painting on canvas.
The original painting, by Jeffrey Smart, is oil paint on canvas.
Oil on canvas.
A diptych.
"Oil on canvas" is a phrase that refers to a singular noun, describing it. This noun, of course, is "painting." A painting is an object composed of oil on canvas. As such, it would be better to avoid pluralizing "oil on canvas" because there is a word much better suited to being pluralized in its stead. "Oils on canvas" lacks the proper meaning, and "oil on canvasses" sounds silly. Simply write that there are paintings (plural) of oil on canvas.
It is an oil painting on canvas.
It is an oil painting on canvas.