APA (7th ed.) Citation

O'Donnell, W. R., & Todd, L. (1991). Variety in contemporary English. Harper Collins Academic.

Chicago Style (17th ed.) Citation

O'Donnell, W. R., and Loreto Todd. Variety in Contemporary English. London: Harper Collins Academic, 1991.

MLA (9th ed.) Citation

O'Donnell, W. R., and Loreto Todd. Variety in Contemporary English. Harper Collins Academic, 1991.