U.S. refiners, many of whom have enjoyed strong profitability due to the wide disparity between domestic and global crude oil prices, continue to do all they can to exploit the U.S. shale boom and secure access to cheap domestic crude oil.

In addition to the traditional mode of transport – pipelines – a handful of refiners have invested heavily in rail and other infrastructure assets, as well as signed deals with third-party transportation providers, to boost the flow of cheap inland crudes to their refineries across the country. Let's take a closer look at two refiners that are going above and beyond merely boosting their usage of domestic oil.

Valero
First up is San Antonio-based Valero (VLO -0.80%), which recently ordered 5,320 new rail cars to move discounted inland crudes to its refineries in Louisiana and California. Of the new rail cars, 1,600 will be coiled cars to deliver anywhere from 25,000 barrels per day to 30,000 barrels per day of undiluted bitumen to the company's St. Charles refinery in Louisiana.

The new rail cars, which cost the San Antonio-based refiner about $750 million, may also be used to move heavy sour Canadian crude oil to the company's Wilmington refinery in California. In addition, Valero announced in March that it will construct a 70,000 barrel per day crude oil offloading facility at its Benicia refinery in California. The project, expected to cost about $30 million, will allow the company to substitute more expensive foreign crudes with cheap domestic oil.

Phillips 66
Next up is Phillips 66 (PSX -3.71%), which recently said it will boost shipments of cheap domestic crudes to its refineries across the country by as much as 130,000 barrels a day, as it joins forces with third-party operators to deliver U.S. and Canadian crudes via pipeline and rail. 

"We are aggressively pursuing increased access to advantaged crudes in North America by partnering with leading third-party transportation providers and better leveraging our own system capabilities," said Greg Garland, chairman and CEO of Phillips 66.

The company has a deal in place with Enbridge Energy Partners (EEP), set to go into effect this month, which will allow rail shipments of Bakken crude oil to the company's East and West Coast refineries. The rail cars will be loaded at Enbridge's terminal in Berthold, N.D., and shipments could ramp up to 35,000-45,000 barrels a day by the fourth quarter.

In addition, Phillips inked a deal with Targa Resources Partners (NYSE: NGLS) last year, which will provide rail-unloading and barge-loading services for crude shipments to the company's Ferndale, Wash., refinery. And another agreement with Magellan Midstream Partners (MMP) will provide the company's Ponca City, Okla., refinery with greater access to crudes from the nearby Mississippi Lime play, starting in late 2013.

Final thoughts
While investors are concerned about the recent narrowing of the spread between domestic crude oil, benchmarked to West Texas Intermediate (WTI), and Brent, the global benchmark, and its impact on Phillips' and Valero's profitability, there is good reason to believe the spread should widen back out to healthier levels by late this year or early next year.

Though a host of new pipeline projects slated to come on line this year should relieve the downward pressure on WTI prices, the sheer scale of U.S. oil production suggests that the additional takeaway capacity provided by these projects will likely prove insufficient in maintaining a narrow spread, at least in the short term.