– The Commerce Department has opened the door to more U.S. oil exports as long as the crude is lightly processed, tempering the impact of a law that banned most overseas petroleum shipments for the past four decades.

The department widened its definition of a refined product eligible for shipping to customers abroad. That means more of the oil being pumped from U.S. shale formations may be eligible for export after being run through small-scale processing units.

The Commerce Department issued its ruling after Pioneer Natural Resources Co. petitioned for approval to export a type of ultralight oil that had been stripped of lighter gases to make it less volatile for transport — a minimal level of processing known as stabilization. The ultralight oil, known as condensate, has been abundant in shale formations during the drilling boom, leading to oversupplies on the Gulf Coast.

"It's a crack in the door which has otherwise been shut for 40 years," said Harry Tchilinguirian, head of commodity markets strategy at BNP Paribas in London. "If approvals for condensate exports are extended to more companies, it'll benefit U.S. producers and processors in Asia, particularly in Singapore and South Korea."

Any oil that has been processed through a distillation tower — a preliminary form of refining — is no longer defined as crude oil, and therefore is eligible for export, said Jim Hock, a Commerce Department spokesman, in a statement this week.

Pioneer uses a distillation unit to stabilize oil it produces in south Texas, most of which is condensate.

The Commerce Department "recently confirmed our interpretation that the distillation process by which our … condensate is stabilized is sufficient to qualify the resulting hydrocarbon stream as a processed petroleum product eligible for export without a license," Pioneer said.

"It's not exactly going to be a game changer but it's certainly the next step in providing the market with some relief," said Robert Campbell, head of oil products research at Energy Aspects, a London-based research firm.

"There are certainly a lot of inexorable economic forces that suggest the U.S. is going to relax the export ban in the long term," said Ric Spooner, a chief strategist at CMC Markets in Sydney, Australia.

The Pioneer approval is expected to spur additional applications for exports, Morgan Stanley analysts led by Adam Longson wrote in a report Wednesday. If more overseas sales are allowed, U.S. condensate could find its way to Asia, from which companies can produce naphtha used in the petrochemical industry, BNP's Tchilinguirian said.

"A lot of condensate splitting capacity is in Asia and more will be added this year," he said. "Some of the Asian processors would have been wondering where the condensate is going to come from."

The U.S. has restricted most crude exports since 1975, in response to the Arab oil embargo. Shipments to Canada are an exception, and those averaged 246,000 barrels a day in March, the highest level since 1999.

"It is certainly the first step toward the lifting of the ban on U.S. crude exports and will be welcomed by the oil world," said Ehsan Ul-Haq, senior market consultant at KBC Energy Economics in Walton-on-Thames, England. "It comes at a time when geopolitical skirmishes have added more than $10 a barrel of risk premium to oil prices."

U.S. oil producers such as Continental Resources Inc. and ConocoPhillips have been clamoring for an end to the restrictions as shale production has brought a surge in North American petroleum supplies. U.S. crude production has jumped 45 percent since the start of 2012, driven by horizontal drilling and hydraulic fracturing in places including North Dakota, eastern Montana and Texas.

Supplies on the Gulf Coast rose to more than 215 million barrels in May, the highest level on record, according to Energy Information Administration data. Much of that supply has been in the form of lighter crude, and arrived after Gulf Coast refiners made expensive upgrades to their plants to process heavier crudes from places such as Alberta and Mexico.

The Commerce Department's willingness to qualify more lightly processed crude for overseas shipments should lead to even wider approval of crude exports, said Sen. Lisa Murkowski, R-Alaska. The decision "is a reasonable first step that reflects the new reality of our energy landscape," she said.