The full text of Joseph Fletcher's classic work is available as a google book.

http://books.google.co.uk/books?id=Y4759nkMFq0C&pg=PA34&lpg=PA34&dq=situation+ethics+and+existentialism&source=bl&ots=leKW8Sb5cK&sig=O1lqduzdsnEScc476zUtJeOZ74s&hl=en&sa=X&ei=-TRwUpVrhMrRBfP2gbgK&ved=0CGoQ6AEwCA#v=onepage&q=situation%20ethics%20and%20existentialism&f=false