As General Motors Corp. drove into a financial ditch, its trip to bankruptcy court was greased by $33 billion in loans from the U.S. Treasury and from Export Development Canada, a state-owned enterprise. Such loans to bankrupt companies, known as debtor-in-possession financing, can be notoriously expensive. Rates, including fees, reached as high as 20 percent in February and generally remain in the low to mid-teens.

GM won’t be paying nearly market rate on its credit, though. The U.S. and Canadian governments, which will own a combined 70 percent of the new auto company expected to emerge from bankruptcy, perhaps as early as July, have provided it with some of the cheapest DIP financing in history. Neither the company nor the Treasury would comment on the details. The Treasury...