Oates v. National Bank is a United States Supreme Court case that was decided in 1879. The case involved a dispute between the National Bank of the City of New York and the plaintiff, William Oates. Oates had been a stockholder in the bank and had loaned it money. When the bank failed, Oates sued to recover the money he had loaned. The Supreme Court held that the bank was liable to Oates for the money he had loaned. The Court reasoned that the bank had received the money from Oates in good faith and had not acted fraudulently. The Court also held that the bank was liable for the money even though it had not been repaid. The Court reasoned that the bank had received the money from Oates in exchange for a promise to repay it, and that the bank had not fulfilled its promise. The Court's decision in Oates v. National Bank established that banks are liable for money they receive from customers in exchange for a promise to repay. This decision has been cited in numerous subsequent cases involving banks and their customers.

Justice Field delivered the dissenting opinion in Oates v. National Bank, arguing that the majority's decision was contrary to established precedent and would lead to confusion and uncertainty in future cases. He argued that a bank could not be held liable for failing to pay out funds on an unenforceable contract because it had no legal obligation or duty to do so. The court should have instead focused on whether there was any fraud or misconduct by either party involved in the transaction, which would have been grounds for holding the bank accountable under existing law. Furthermore, Justice Field noted that if banks were held responsible for such contracts then they would be forced into a position of having to investigate every customer’s financial situation before entering into any agreement with them; this could potentially create more harm than good as it may discourage people from seeking banking services altogether due to fear of being denied based on their creditworthiness. Ultimately, he concluded that while banks must act responsibly when dealing with customers' money, they cannot be expected nor required by law to guarantee payment against invalid agreements made between two parties without their knowledge or consent.