Delta Air Lines said on Monday that it had agreed to buy a refinery near Philadelphia from ConocoPhillips to offset the risk of higher jet fuel prices.

Delta said that it would spend $150 million to acquire the Trainer refinery, which has been shuttered for six months, after receiving $30 million from the state of Pennsylvania as part of a deal to support job creation.

The airline said it would spend $100 million more to refurbish the plant to increase its output of jet fuel.

Richard H. Anderson, Delta’s chief executive, said the investment was a modest one, equivalent to the list price of a new wide-body plane like a Boeing 777. The company estimated that it would reduce its annual fuel expense by $300 million, once the refinery was refurbished and operating again.