Wall Street’s generous supply of funds to U.S. oil drillers helped create the American energy boom. Now that same access to easy money is keeping them going, despite oil prices that are languishing around $60 a barrel.

The flow of money into oil has allowed U.S. companies to avoid liquidity problems and kept American crude production from falling sharply. Even though more than half of the rigs that were drilling new wells in September have been banished to storage yards, in mid-May nearly 9.6 million barrels of oil a day were...