At first, bitcoin was a way to make payments without banks. Now, with more than $100 billion stashed in digital currencies, banks are debating whether and how to get in on the action.

Goldman Sachs CEO Lloyd Blankfein tweeted Tuesday that his firm is examining the cryptocurrency. Other global investment banks are looking into facilitating trades of bitcoin and other cryptocurrencies, according to industry consultants. Bitcoin has surged more than 300% this year, drawing the attention of hedge funds and wealthy individuals.

"They're clearly receiving interest from their clients, both from retail investors and on the institutional side," said Axel Pierron, managing director of bank consultant Opimas. "It's highly volatile, it's highly illiquid when you need to trade large volumes, so they see the opportunity for a new asset class which would require the capability of a broker-dealer."