Valero Energy's (VLO 0.27%) first quarter earnings report showed a 30% rise year in earnings per share year over year. Moreover, the company's gross profit margin also slightly improved to 9%. What drove up its earnings in the past quarter? Here are three charts explaining the company's first quarter results.

Source of data: Google Finance

The company's profitability slightly improved in the past quarter, as indicated in the chart above.

In comparison, Marathon Petroleum (MPC 0.80%) didn't show an improvement as its profit margin dropped below 5% in the first quarter of 2014. One reason for this lower profitability is a narrower spread between Brent and WTI crude oil. Usually, as margins contract, refiners become less profitable. The chart above shows the Brent-WTI spread diminished by half from nearly $18 per barrel in the first quarter of last year to $9.4 per barrel in the first quarter in 2014.

So why didn't Valero Energy's profitability decline in the past quarter? Because the company's other types of crude, such as Maya and Mars, which are considered sour crudes, had a staggering increase in their discounts over Brent oil. The improved margins on these types of crude oil have more than offset the decline in the Brent-WTI spread. One way to look at the difference in types of oil is by examining the various regions the company operates in.

The second chart breaks down the company's throughput volume and operating profit for its four main regions.

Source of data: Valero Energy

As you can see, during the first quarter of 2014, the Gulf Coast accounted for the majority (58%) of the company's throughput volume. This region is also the second most profitable at a $6.19 per barrel of operating income. The two least profitable regions, North Atlantic and West Coast, account for only a quarter of the total volume. Therefore, the impact of these regions was lower than the effect the Gulf Coast and Mid-Continent had on Valero Energy's earnings in the first quarter.

Moreover, the two highest growing regions in terms of throughput volume are the Gulf Coast and Mid-Continent at 11% and 7%, respectively, as indicated in the chart below.

Source of data: Valero Energy

The chart shows the year-over-year percent changes in throughput volume and operating income per barrel by region. In the past quarter, the Gulf Coast region was not only the highest growing region in terms of volume, but it also showed the sharpest rise in operating income -- a 34% gain. Looking forward, the company expects to further increase its oil operations in the coming quarters as the demand for oil during driving season is projected to rally. Finally, the company's capital expenditure is set at $3 billion for 2014 -- nearly 9% higher than in 2013. The higher capex is likely to keep pushing Valero Energy's throughput volume higher.

Bottom line
The rise in Valero's throughput volume in the Gulf Coast was a major factor in its higher bottom line, due to improved throughput margins in that region. Furthermore, the expected rally in demand for gasoline is likely to be a catalyst in the coming quarters. Finally, if the company keeps augmenting its operations in the Gulf Coast this could improve its profit margin in the near future.