The Rio Vista Gas Field is a large natural gas field in the Sacramento–San Joaquin River Delta in northern California, adjacent to Rio Vista, California. Discovered in 1936, and in continuous operation since, it has produced over 3.6 trillion cubic feet (100 km3) of gas in its lifetime, and retains an estimated reserve of approximately 330 billion cubic feet (9.3×109 m3). In 2008 alone, the most recent year for which data was available, it produced 18 billion cubic feet (510,000,000 m3) of gas. Spanning portions of three counties and covering over 29,000 acres (120 km2), it is the largest natural gas field in California, and one of the fifteen largest in the United States.