APA (7th ed.) Citation

Cather, W. (1999). O pioneers! (1. publ. as an Oxford World's Classics paperback.). Oxford Univ. Press.

Chicago Style (17th ed.) Citation

Cather, Willa. O Pioneers! 1. publ. as an Oxford World's Classics paperback. Oxford [u.a.]: Oxford Univ. Press, 1999.

MLA (9th ed.) Citation

Cather, Willa. O Pioneers! 1. publ. as an Oxford World's Classics paperback. Oxford Univ. Press, 1999.