Peak oil, the idea that global crude oil production peaked out in 2006 at 70 million barrels a day, is pretty widely accepted as fact. If demand was dropping along with projected supply, there would not be as much of a problem. But at least one organization, the International Energy Agency (IEA), predicts that declining supply and rising demand from China means that the price of a barrel of oil will hit $135 by 2035.

Peak oil doesn’t just refer to the fact that the top of production has been achieved, but that a peak in prices is the new normal.

It’s worth noting that the dispute over peak oil comes from oil companies that believe that if we just allow offshore oil drilling, we can add significantly to global supply. But the IEA predicts that most of the rising Chinese demand for oil will be satisfied through increased production from Canada’s tar sands and increased production of natural gas liquids.

So does this mean you should buy shares of the biggest suppliers of these unconventional energy sources?

To figure that out, it helps to look at the leading publicly traded providers of these energy sources. Specifically, we’ll examine their historical performance and their market values relative to their earnings prospects. The goal is to figure out whether these companies could make good peak oil investments.

As far as tar sands go, the world’s capital is the Canadian province of Alberta. It houses 173 billion recoverable barrels of tar sands worth $18.5 trillion at today’s price of $107 a barrel. Recovering all those barrels causes tremendous environmental damage — by tearing up the ground and spewing more CO2 into the environment. And as Alberta’s tar sands market leader, Suncor Energy (NYSE: SU) will get a big share of its profits.

Suncor’s financial performance has been good but the stock is not cheap on a Price/Earnings to Growth basis. In the last year, sales spiked 38% to $35.7 billion while net income rose a whopping 169% to $2.8 billion. Suncor’s PEG of 2.3 is way above the 1.0 I think is fair — on a P/E of 25.7 to earnings expected to grow 11.2% to 2.92 in 2012. But if that 2012 forecast is too modest — Suncor’s 2011 earnings grew 51% — then the stock could be a great way to play peak oil.

Meanwhile, when it comes to natural gas liquids, the good news is that production is up 11% to 284 trillion cubic feet. Many of the major oil companies are natural gas liquids or NGL producers including BP plc (NYSE: BP), Conoco Phillips (NYSE: COP), and ExxonMobil (NYSE: XOM). ExxonMobil produces 1.8 million barrels of NGL a day, BP produces 670,000 NGL barrels a day. And at 363,000 NGL barrels per day, Conoco is the smallest of the three.

But these stocks are not focused solely on NGL. For that I would look at Provident Energy (NYSE: PVX), an Alberta-based NGL extractor and distributor. Its revenues rose 12% to $1.69 billion and its earnings were up 19-fold to $104 million in the last year. And at a PEG of 1.7 — on a P/E of 24.4 and 14.3% earnings growth to $0.56 in 2012 — the stock is not cheap.

But if you want to play peak oil, I would consider putting funds into Suncor and Provident.

Peter Cohan has no financial interest in the securities mentioned.