His most famous portraits were made using oil paints. He also did finished portrait drawings. And he painted many landscapes, city scenes, and casual views of friends as well various anatomical studies. In other words, Sargent was a hugely prolific artist.
One aspect of his output that I find worth a blog post is casually-done, sketchy even, oil portraits of women. Some of these are shown below in roughly chronological order.
She was a favorite subject at a time he visited the isle of Capri. I think this is one of Sargent's finest works.
A borderline sketch, the face fairly carefully realized while the rest of the canvas is little more than blocked in.
Sketch portrait of one of Sargent's friends.
Just enough facial detail to be quite convincing.
Madame X in a casual pose.
A flattering sketch that's interesting in terms of Sargent's choice of placement of light and shade.
Another portrait where only the face was given consideration.
A very nice study, though her mouth seems too small.