Study 16 hours and what do you get? Another day older and deeper in debt.

Okay, that's not nearly as gripping a lyric as Tennessee Ernie Ford's classic coal-mining ballad, "16 Tons."

But for college students and their families, the deep-in-debt part sounds just right. Every day that students stay in school, the more money they owe.

Now you're being encouraged to borrow even more. Lenders are offering "alternative" or "private" loans on top on your federal student loans.

A one-year federal student loan is currently capped at $2,625 to $5,500 for undergraduates, depending on which year of school you're in.

That's often not enough to fill the gap between the money you have and the cost of the school you want to attend.

Parents can borrow the rest of the money through the federal PLUS program (Parent Loans for Undergraduate Students). But they have to start repaying PLUS loans right away.

Enter the private loan, to compete with PLUS. It's more expensive than PLUS, but payment can be deferred until the student leaves school.

Also, private loans generally are made to students rather than parents, which many parents like. The parents may have to co-sign, so they're responsible if their son or daughter can't pay. But the student carries the principal burden.

Private loans are made two ways: directly through banks or other lenders or indirectly, through college financial-aid offices. Some colleges simply hand out the bank's brochures while others market the loans under their own name. You can borrow the difference between what you got in financial aid and your college's total cost.

When schools enter into joint agreements with banks, they usually negotiate better terms for their students, says George Walter, director of financial assistance for Villanova University in Pennsylvania. The interest rate might be a little lower, or parents might not have to co-sign the loan.

How much you pay for a private loan depends on the terms. Upfront costs usually range from 3 percent to 8 percent, depending on who borrows (parent or student), whether there's a co-signer, how soon repayments start and the borrower's creditworthiness. The fees are deducted from the loan amount.

Variable interest rates range from 7.8 percent to 9.7 percent, again depending on circumstances. Students with co-signers pay less than students without.

Some private lenders charge little or nothing in fees but recoup with a higher loan-interest rate. Citibank's standard loan, for example, currently costs zero up front plus 9.25 percent on the borrowed money.

By contrast, parents using federal PLUS loans typically pay 4 percent up front plus 7.72 percent interest on the money borrowed (the loan rate changes every July 1). PLUS loans are capped at 9 percent. Private loans can go higher if interest rates rise.

A few state student-loan agencies offer private student or parent loans at lower rates--ask your school about it.

Here are some major commercial programs to check for private college loans, in addition to any that your school is tied up with: BankBoston (www.bankboston.com; 1-800-255-8374);

Bank of America (www.bankofamerica.com; 1-800-344-8382); PNC Bank (www.eduloans.pncbank.com; 1-800-762-1001); and Citibank (www.studentloan.com; 1-800-692-8200).

At Citibank, the loan's co-signer is released of responsibility if the student makes the first 24 payments on time, says Bill Beckman, head of the student-loan division.

Chela Financial in San Francisco, also a source of higher-education loans, is promoting a new program called AcademicEdge. Unlike other private loans, this one lets students borrow more than their college's actual cost, at higher interest rates (academicedge.chelafinancial.com, 1-800-282-4352).

Currently, four-year students leave school owing an average of around $13,000, says Scott Swail, associate director of policy at the College Board in Washington. Debt burdens are rising, not only because college costs keep going up but also because so many students choose expensive schools.

"For most families, increased borrowing is the path of least resistance," says Barmak Nassirian, associate executive director of the American Association of Collegiate Registrars and Admissions Officers in Washington.

The banks, by the way, don't just make private college loans. They also handle traditional, federal student loans. In that program, Congress sets the price--and guarantees the lenders a profit.

At this very moment, the lenders' congressional buddies (well greased with campaign contributions) are planning to fatten the industry's profits by changing the way the government subsidizes student loans. Students won't pay more but the taxpayers will, Nassirian says.

Do the colleges, lenders and taxpayers care that students are drifting toward 16 tons of debt?