Gilbert Spencer painted prolifically in oils, producing around 400-500 paintings. To aid navigation, they have been divided into categories by genre. By far the largest group is landscapes, the genre for which he is best known, and which were painted directly, en plein air. Urban landscapes, in which buildings predominate, are grouped separately, together with a handful of interiors and still lifes. Spencer’s other speciality was agricultural scenes. There is occasionally some overlap between these and figure paintings, which were painted from memory and imagination. For the latter, he worked out the composition in pencil and watercolour, which was then squared for transfer to canvas. The small but significant group of Biblical paintings are closest in style and subject to those of his brother, Stanley. War paintings and portraits complete the categories.

Spencer’s usual support was canvas, though he did paint on panel from time to time, in fresco, and once or twice on silk. His preferred supplier was Winsor & Newton, but he bought at least once from Newman, and their canvas stamps can help to date unidentified paintings. His preferred frames were traditional gilt gesso from Alfred Stiles. Spencer’s oil paintings are usually (but not always) signed, and rarely dated.