Advocates of income-sharing agreements, sometimes called human capital contracts, see them as a way to spread risk and prevent students from being locked into dangerously high debt payments. “Affordability is built in,” said Robert M. Whelan Jr., the chief executive of 13th Avenue Funding, a nonprofit company that ran a small pilot test of the income-sharing model with 11 students in California in 2012 and 2013. “Student debt is a crisis, and this is an opportunity to approach it in a different way.”

The idea also intrigues some politicians. Senator Marco Rubio of Florida, who introduced legislation two years ago to clarify the legal framework around the agreements, and Gov. Chris Christie of New Jersey both spoke in favor of them on the Republican campaign trail. Lawmakers in Oregon have been working for three years to develop a test program called Pay It Forward.

Income-sharing agreements operate in a legal gray zone, however. No major regulators have drafted rules specifically to address them, and Senator Rubio’s proposed guidelines never made it out of committee. Financing firms are left largely on their own to tailor their products, fees and disclosures to consumer-protection laws that are designed for traditional loans.

The Consumer Finance Protection Bureau, the federal overseer that many view as the industry’s likely regulator, said it was keeping an eye on the offerings.

“It is important that consumers know up front the costs and risks of financial products,” said Seth Frotman, the agency’s student loan ombudsman. “This generally isn’t the case for income-sharing agreements, which can create challenges for borrowers trying to navigate their repayment options.”

Advocates say they think the concept will gain popularity, and they point to successes in places like Australia, where university students have long repaid their educational costs through income-tax surcharges.

The Obama administration has been more wary. President Obama has focused on making federal student loans more affordable by expanding their income-based repayment options. In December, new rules took effect allowing all federal borrowers to choose a plan that caps their loan payments at no more than 10 percent of their monthly income after graduation. After 20 years of payments — or 10 years for those who work for government organizations or most nonprofits — any remaining balance for undergraduate loans will be forgiven.