Can I Make Audiobooks for Private Use?

Dear Rich: Is it legal to borrow a book from my local library, make my own homemade audiobook, return the book afterwards, and keep the audio files I produced? I only want to make audiobooks for my own personal research and study, but I don't know if this breaks some copyright about making unauthorized copies. These audiobooks are just for my private research. Yes, you're likely violating copyright law; only the copyright owner can create derivative versions. But if you're the only one listening to them and you're not distributing copies, we doubt whether the copyright owners will know or care about your use. It's our little secret!