Clients that traded with Goldman on those terms either bought the index at an above-market level or sold at a below-market level, which put them “underwater” at the start of the trade, the CFTC said in a settlement order with a unit of Goldman it oversees. In settling the case, Goldman admitted that it failed to disclose important pricing details, the order shows.

“As today’s penalty against Goldman demonstrates, the CFTC will aggressively pursue swap dealers that violate these business conduct standards,” enforcement director Ian McGinley said. A Goldman spokesperson declined to comment.

Swaps are financial contracts in which traders agree to exchange payments based on, say, changes in the price of a stock, index or other asset. Buyers can purchase them from a bank such as Goldman, typically paying a fee, expressed as an interest rate, when they enter the trade.

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In the transactions investigated by the CFTC, Goldman traders set the initial price of the swap using the MSCI Europe Australasia and Far East Index’s value on the same day the parties agreed to the trade, regulators said.

Such trades are typically priced on the following day’s value of the index, in order to reduce the risk that banks with more information about the underlying markets could gain an advantage in how the swaps are priced, the CFTC said.

Goldman benefited when it found a client that would agree to same-day swaps because it could enter into related trades that quickly netted a profit, the CFTC said. The bank’s traders didn’t disclose what the CFTC said was an important midpoint price that influenced the buyer’s cost, and sometimes told clients they were getting a better deal than they were, regulators said.

“The ‘preferential’ interest rates that Goldman offered clients to entice them to transact same-day did not fully compensate the clients for the disadvantage at which the client would start” the trade, the CFTC’s order stated.

Goldman tended to target the trade at clients who understood less about how the underlying markets of the swaps worked, the regulator said.

“Communications show that Goldman personnel believed that the less the clients understood about the economics of the same-day swaps, the more profit Goldman could make,” the settlement order said.

Write to Dave Michaels at dave.michaels@wsj.com

This article was published by The Wall Street Journal, a fellow Dow Jones Group title