Oil refining can be a more volatile business than other areas of the energy industry. That's because pricing spreads between domestic West Texas Intermediate crude and international equivalents can shift sharply in any given period. When these margins contract, oil refining is a very difficult business, and corporate profits dry up. This was a significant hurdle last year for refiners such as Marathon Petroleum (NYSE:MPC) and Valero Energy (NYSE:VLO).

This year, it's an entirely different story. Operating conditions have improved substantially, and as a result, so have financial performances across the industry. As you'd expect, the stock prices of these companies have risen in response to the developments.

Shares of Marathon Petroleum are up approximately 33% over the past 52 weeks. While that's certainly a great performance, here are three reasons why the stock could keep rising.

Refining profitability keeps improving
A major reason for Marathon Petroleum's rally over the past year has been significant improvement in its core refining and marketing activities.

In all, revenue grew 4% to $26.9 billion. Second-quarter earnings clocked in at $2.95 per diluted share. This represented 61% earnings-per-share growth from the same period of last year. Refining operating profit surged 39% in the last quarter. This was crucial for Marathon's performance, since the refining and marketing segment is the company's biggest by far, accounting for approximately 92% of total operating profit.

This theme played out across the industry. For example, Valero Energy produced 45% earnings growth in the last quarter. The primary contributor was increased refining volumes. Throughput volumes averaged 2.7 million barrels per day, a nearly 5% increase year over year. Management attributed this to discounted North American light crude oil on the U.S. Gulf Coast.

Integrated structure provides stability
Importantly, Marathon's future will likely not be so heavily reliant on just refining and marketing. The company has a budding midstream business, which will help smooth results and reduce some of the volatility when refining conditions decline.

The benefits of this integrated structure are clear. Marathon Petroleum generated 39% growth in operating profit in its pipeline transportation business as compared to the second quarter of 2013. Management believes its midstream pipeline business helps the overall company maintain operational flexibility. With an integrated model, Marathon Petroleum can reap increased efficiency.

The integrated system also allows Marathon to capture higher product price realizations in key markets, which actually helps the refining business.

Increasing shareholder rewards
After providing earnings results last quarter, Marathon Petroleum announced a large increase to its shareholder rewards initiatives. The company raised its dividend by 19% and increased its share buyback authorization by $2 billion. This was an addition to the remaining $709 million in the company's existing share repurchase plan.

Management is committed to returning a large portion of cash to investors through both dividends and share repurchases. It has significantly increased its capital allocation programs since becoming an independently traded company, and since its 2011 spinoff, management has increased its share buyback authorization four times.

At recent prices, Marathon yields 2.2%, which is about on par with the broader stock market. However, the company has increased its dividend by 35% compounded annually since its spinoff, making the income potential very attractive.

Marathon Petroleum may still have room to run
This is a good time to be an oil refiner. Favorable pricing spreads have improved margins, which is significantly boosting profitability for Marathon Petroleum. Earnings per share came in strong in the last quarter, driven by improving refining and the company's integrated business model.

Management is sharing the company's success with investors via a significantly expanded share repurchase authorization and a hefty dividend raise. Through these initiatives, Marathon Petroleum offers compelling cash returns in addition to its stock price performance.

Improving refining, the budding transportation business, and compelling cash returns are three reasons why we could see this stock march higher.