Quote from 1955: A prelude to the Works in Oils list:

"The pictures have been arranged by years in two lists: portraits in the first section, numbered consecutively according to year; works other than portraits in the second list. The dates given here are placed according to the best obtainable information. In many instances they conflict with those given in older publications, a difficulty compounded by the fact that the artist himself frequently misdated his paintings. His habit was to add the date and signature not when they were done but when they passed out of the studio to an exhibition or into the hands of a purchaser. In later years he was often asked to sign and date early works and his guesses sometimes landed a few years wide of the mark. In each case the last owner known to me has been given to aid identification."

 Note from the Pragmatic Romanticist:

I have combined both portrait and non-portrait listings under the same year. CMM numbered both the portraits and the non-portraits (the non-portraits with a leading K) and I have retained this convention.
 

Sargent's Works in Oil 1874 - 1879 Age 18 to 23  1880 - 1889 Age 24 to 33  1890 - 1899 Age 34 to 43  1900 - 1909 Age 44 to 53  1910 - 1919 Age 54 to 63  1920 - 1925 Age 64 to 69  Undated Oils   Statistical Chart  June 9, 2000 - For the left-brained art lover.