I found this great link and thought it will be useful for you. Most especially if you are studying petroleum/petro-chemical/chemical science/engineering.
It is also a great resource for certifications and scholarship tests in the field. There are lot of e-books that you can download free-of-charge from through the link.
Click below for different Petroleum Engineering Books for Certifications and Scholarship Tests
Petroleum Engineering Books for Certifications and Scholarship Tests (http://www.4shared.com/dir/7091707/f73d923f/sharing.html)