In choosing between two good textbooks for an honors mathematical studies course, Carnegie Mellon University professor Robert Pego employed a bit of economics.

He chose the one that lists for about $60 hardbound, not the one that lists for $166.

"Why should I make students pay that?" he said.

Dr. Pego is among faculty members nationwide who are paying attention to how much textbooks cost and trying to do something about it.

He and hundreds of other faculty members have signed a statement of intent to use free, online, open-source textbooks whenever academically appropriate.

The statement is part of an effort by the Student PIRGs -- Public Interest Research Groups -- which expect to announce tomorrow that they have reached 1,000 faculty signatures.

Like college tuition, the price of textbooks has soared faster than inflation. From 1986 to 2004, textbook prices nearly tripled, according to a Government Accountability Office report in 2005.

The GAO said the best explanation for the increase is the development of new products accompanying the books, like CDs and other supplements.

Nationwide, the GAO figured that textbooks were about a fourth of the cost of tuition and fees at four-year public colleges and universities and as much as three-quarters of the cost of tuition and fees at two-year public institutions.

Carnegie Mellon estimates that books and supplies cost students $966 a year. Pitt estimates it at $600 to $1,000 a year.

Nicole Allen, Student PIRGs textbook project director, said textbook prices for a course can exceed tuition at community colleges in California.

"It can really be a tipping point expense for lower- and middle-income students. They have to face a difficult decision whether to drop out, take on more loan debt or undercut their own learning by forgoing purchasing textbooks," she said.

Examples of some of the available open textbooks, which generally are free if used for noncommercial purposes, are on the Web site, www.maketextbooksaffordable.com.

The list includes texts on physical oceanography, economic analysis, physics, linear algebra, probability and programming.

The Student PIRGs also are pushing Congress to address the textbook price issue.

The House version of the Higher Education Reauthorization Act, which is in conference committee, would require publishers to tell faculty the price of the book, the history of revisions and whether any lower-cost formats are available.

It also would require publishers to offer textbooks separately rather than only bundled with other materials like CDs. And it would require schools, to the "maximum extent practical," to put the list of required texts in registration materials so students would have time to shop for lower prices.

J. James Bono, a doctoral student and teaching fellow in English at the University of Pittsburgh who signed the statement, said the total cost of the books for just one of his graduate level classes he took was $400 if purchased new.

Last week, he was headed to Hillman Library to pick up a box of 15 to 20 books he had requested. He also belongs to the New York Public Library, which has an on-demand print service for materials in the public domain.

But, he said, "the lead time is sometimes a problem."

For students in the writing for the public class he teaches, Mr. Bono said, "I try to use open source and freely available materials when I can."

He still has a textbook for the class he teaches, but it replaces a more expensive book and has been in use for a while, so students are more likely to find a used copy. Amazon.com lists the book at $59.60 new, but also shows used copies as low as $7.99. He supplements the book with freely available materials.

Of his seminars, he said, "I've noticed my faculty members increasingly using online resources and distributing them digitally."

Juan Manfredi, a math professor at Pitt who signed the statement, said he thinks demand will shift toward customized materials that use only parts of big textbooks. He compares that to the music industry, in which many consumers buy individual songs over the Internet rather than a whole CD.

"I don't like the fact that regular calculus books cost $150," he said. "They pack everything into the book -- the material for calculus 1, 2 and possibly 3. Some students might not take the three courses."

This term, his honors class on introduction to analysis is using a regular textbook because Dr. Manfredi couldn't find a suitable alternative. Amazon.com sells the book for about $112.

For some other courses, he has turned to a publishing house that offers books in the public domain for $10 to $30.

"I always look for alternatives," he said. "These days, with easy Internet access, there are more and more resources available. We have more and more opportunities to provide affordable information.

"I think it's only a matter of time before we can rely essentially on some sort of electronic distribution of textbook materials."