Citadel, a $28 billion hedge fund titan, last year traded enough natural gas to meet more than a month of U.S. residential demand, becoming an unusual force in a market dominated by merchants, energy producers and utilities.

Its trading of physical gas makes Chicago-based Citadel, led by Ken Griffin, unique among hedge funds. Other funds limit their gas trading to futures and options contracts, which allow price exposure without the complexity of handling fuel. Citadel buys and sells actual molecules over North American pipelines after establishing a physical gas business in 2014.