The numbers sound huge, but what do they mean? That's the big question after the United States Geological Survey bumped up the heavy oil reserves in Venezuela's Orinoco region to 513 billion "technically recoverable" barrels.

The agency said this mother-lode is "the largest accumulation ever assessed by the USGS." But it's unlikely to change the world rankings of oil producers.

On the industry-accepted Oil & Gas Journal list, Saudi Arabia comes first, with 264 billion barrels of largely easy flowing crude, followed by Canada's 175 billion barrels of oil, mostly from the oilsands. With 99 billion barrels, Venezuela trails Iran, Iraq and Kuwait.

"It all depends on how you count your reserves, and in Canada our data are open, transparent and reviewable. You can even look at the drilling logs and core samples," Greg Stringham, vice-president of the Canadian Association of Petroleum Producers, said Monday.

Canada's tally starts off with the 1.7 trillion barrels in place. Technology challenges in recovering the tar-like bitumen drop the recoverable number to 311 billion barrels, and the hard economics of bitumen recovery drive that down further to 170 billion barrels. All projects currently running have reserves of 21 billion barrels.

"So let's look at the context, and see that you are comparing apples to apples," Stringham said.

Venezuelan President Hugo Chavez and his government have drawn up plans to bring foreign investors, including companies from China and India, into the region. U.S. oil firms have continuing disputes with Chavez, and Venezuela's shipments to the U.S. have plummeted.

Mexico has also cut shipments as its oilfields decline.

"So for Alberta, our interest is that the Gulf Coast refineries want Canadian heavy oil. And if we can move into those markets and sign long-term contracts, and develop a secure relationship in these markets, then we will be in there," Stringham said.

Even if Venezuela began increasing oil shipments again to the United States, it would now face Canadian competition.

Mike Percy, dean at the University of Alberta's business school, and Joseph Doucet, Enbridge professor of energy policy at the business school, said Alberta doesn't have to worry about the Venezuelan discovery, yet.

"At the end of the day, it's not a game-changer," Percy said.

That's because Venezuela has historically been unstable, with a state-owned oil company that has been "extraordinarily inefficient," he said.

"Although they may have the recoverable reserves, they have neither a regulatory regime nor the degree of stability that would lead outside firms to invest hundreds of billions of dollars to recover them," Percy said.

Alberta's stability and location make it much more appealing than Venezuela and other areas with large oil reserves, he said.

"There may be oil out there, but a lot of it is in jurisdictions where there's not the same degree of stability that you see here, and stability . . . is vitally important for firms to make long-term investments to recover those resources," Percy said.

"In Venezuela, you can put (money) in, but the odds are, you're not getting it back."

Doucet said revisions of estimates are interesting markers to watch, "but in terms of actual impact on market prices, on investment and things like that, we really look to issues of cost and technology."

"The situation in Venezuela is significantly different than Alberta, given the political environment and the uncertainty there, so that also suggests that, while there may be more oil there than some people had thought, there's a big, big leap from there actually being more oil to having more oil produced. That is, at the end of the day, what really matters."

What is actually produced also depends on many factors, such as strategies to cut greenhouse gas emissions and what can be accessed through mining operations, Doucet added.