APA (7th ed.) Citation

Piper, H. B. (2009). Oomphel in the Sky. Project Gutenberg.

Chicago Style (17th ed.) Citation

Piper, H. Beam. Oomphel in the Sky. Project Gutenberg, 2009.

MLA (9th ed.) Citation

Piper, H. Beam. Oomphel in the Sky. Project Gutenberg, 2009.

Warning: These citations may not always be 100% accurate.