I'd say Kaplan MCAT prep book is really great for the science components of the OAT. For verbal practice, practice, and practice. With the Quant. I bought a couple of books on mathematic skills and review. I was doing badly with word questions so one of the books I bought was basically on how to solve word math questions and that helped a lot. I also referred to Top Score and OAT Achiever to get some practice on the computer.