A man bathes in crude oil. REUTERS/ Stoyan Nenov The banks that energy companies depend on for loans are pulling back from the sector.

Oil prices plummeted in late 2014, and they have remained low. Energy companies often borrow money using their reserves as collateral.

With the value of those reserves falling as commodity prices slide, the companies will not be able to borrow as much in the future and may have to repay parts of some existing loans.

Banks are now basing their lending decisions on an oil price of $48 a barrel, according to a survey by Macquarie. That price was $77 a barrel at the end of the last year, according to Bloomberg.

The CEO of Whiting Petroleum said earlier this month that the maximum amount of money it could borrow may drop to $3.75 billion from $4.5 billion as a result of the changes, according to the Bloomberg report.

A recent survey by the law firm Haynes Boone LLP meanwhile found that financial institutions and private-equity firms expected a fall in "borrowing base redeterminations," or the value of companies' assets that can be posted as collateral.

In addition, bank regulators are paying closer attention to the sector. According to Emily Glazer, Ryan Tracy, and Rachel Louise Ensign at The Wall Street Journal, big banks are facing pressure from Washington on their energy portfolios.

Regulators from the Office of the Comptroller of the Currency, the Federal Reserve, and the Federal Deposit Insurance Corp. met with bankers in Houston earlier this month to discuss reserve-based lending requirements, according to the report.

The result is tougher standards for loans, potentially higher prices for borrowers, and a quick path to Chapter 11 for struggling companies that are pushed closer to defaults thanks to the plummeting price of their underlying assets.