PORTLAND, Ore. -- College can cause a chronic case of sticker shock.

In addition to skyrocketing tuition comes the cost of textbooks, which the U.S. Government Accountability Office says has risen twice as fast as inflation for two decades. Students now spend nearly $700 or more each year on textbooks.

But there is good news. A federal law that went into effect this summer requires publishers to tell professors how much their textbooks cost and mandates that schools identify books needed for each class at registration so students have time to shop around. Here are ways to cut textbook costs:

At the store

Most textbooks are still sold through the campus bookstore, according the National Association of College Stores. The trade group recommends shopping early, buying used and checking your store's website for deals.

Also try the stores' Facebook pages and Twitter feeds for specials. And remember to recoup some of your cash at the end of the term by selling your books back to the store.

E-reading

The electronic-reading format is growing but remains limited, aside from books whose copyright has expired, some of which can be found free through Google Books, Project Gutenberg and other websites.

Flat World Knowledge, founded by former textbook industry leaders, provides free online access to some textbooks plus print-on-demand, audio and downloadable versions.

This fall, it is adding versions for electronic book readers. The company said its customers routinely spend 80 percent less than they would on traditional textbooks. Also offering versions for e-readers are sites such as Coursesmart.com, which also provides online tools for highlighting or taking notes in electronic books.

Digital books were available for about 15 percent of courses last year, according to the National Association of College Stores.

Experts expect the format to keep expanding.

Rent

Numerous websites -- Chegg, BookRenter, College Book Renter and others -- have popped up to lend textbooks for a fee. The services typically operate through the mail, like Netflix for books.

Barnes & Noble also plans to expand its textbook rental program.

Renting allows students to read a printed book without extra equipment and -- in many cases -- still highlight and take notes in the text.

BookRenter, which says its customers can save 75 percent off buying a book, now offers rental services in partnership with more than 250 campus bookstores.

Some colleges also loan textbooks through campus libraries but availability can be limited.

Compare

The new law guarantees students easy access to the ISBN, the international standard book number that identifies the textbook, making it easier to comparison shop.

Try Amazon.com, efollet.com, iChapters.com and Half.com, which is part of eBay. Also check sites that let students search several retailers at once, such as Bigwords.com and Bestbookbuys.com.

At Campusbooks.com, you can find the best prices for both buying books at the beginning of the term and selling them at the end.