We are an interstate natural gas transmission company that owns and operates a natural gas pipeline system extending from Texas, Louisiana, Mississippi and the Gulf of Mexico through Alabama, Georgia, South Carolina, North Carolina, Virginia, Maryland, Delaware, Pennsylvania and New Jersey to the New York City metropolitan area. We also held, until December 31, 2019, an approximate 45 percent interest in Cardinal Pipeline Company, LLC (Cardinal), an intrastate natural gas pipeline located in North Carolina. Our principal business is the interstate transportation of natural gas which is regulated by the Federal Energy Regulatory Commission (FERC). At December 31, 2019, our natural gas pipeline, which extends from Texas to New York, had a system-wide delivery capacity totaling approximately 17.4 MMdth of gas per day. During 2019, we completed four fully-contracted expansions, which added more than 0.6 MMdth of firm transportation capacity per day to our pipeline. In addition, we added approximately 0.1 MMdth of firm transportation capacity per day by splitting long haul capacity into Gulf Coast capacity and Southeast and Northeast capacity. The system is comprised of approximately 9,800 miles of mainline and branch transmission pipelines, 57 compressor stations, four underground storage fields and one liquefied natural gas (LNG) storage facility. Compression facilities at sea level rated capacity total approximately 2.3 million horsepower.
Operating Income for the three months ended March 31, 2020 was $339.8 million compared to $290.3 million for the three months ended March 31, 2019. The increase in Operating Income of $49.5 million (17.1 percent) was primarily due to higher Natural gas transportation revenues in the first three months of 2020 compared to the same period in 2019, and a favorable change in Operating Costs and Expenses, as discussed below. Net Income for the three months ended March 31, 2020 was $278.0 million compared to $229.7 million for the three months ended March 31, 2019. The increase in Net Income of $48.3 million (21.0 percent) was mostly attributable to the increase in Operating Income, as discussed below.