Several books, including the Kaplan OAT course book/flash cards/study sheets, Princeton Physics OAT review book with 2 practice online exams and drills/summary sheets for every test section, OAT destroyer books for Biology, General Chemistry, Physics, Quant. Reasoning, and O-Chem. Also a few other books... Basically, a stack of books that really helped me a lot in taking the OAT exam.