The country's fourth biggest refiner announced today it was buying up billions of dollars' worth of stock. Marathon Petroleum (NYSE:MPC) said the board of directors approved the addition of $2 billion in share repurchase authorization to the already existing plan, which still has $1.34 billion remaining on it.

The buyback program will run through September 2015, and the refiner said it would utilize all the tools in its toolbox to do so, including open market repurchases, negotiated block transactions, accelerated share repurchases, or open market solicitations for shares, some of which could be effected through Rule 10b5-1 plans. Of course, the program could also be discontinued at any time.

Saying the buyback announcement underscores the refiner's commitment to shareholders, Marathon Petroleum President and CEO Gary R. Heminger said, "Our focus continues to be returning capital to our shareholders on a sustained basis while making value-enhancing investments in the business."

In addition to Marathon's seven-refinery operations, which has capacity of approximately 1.7 million barrels per calendar day, it sales branded gasoline through 5,000 retail outlets in 17 states; owns and operates the nation`s fourth-largest convenience store chain, with approximately 1,470 convenience stores in nine states, via its Speedway subsidiary; and owns, leases, or has ownership interests in approximately 8,300 miles of pipeline.