Canadian energy companies operating offshore could face new regulations in the aftermath of the Gulf of Mexico oil spill and the more aggressive oversight may put their shares at risk.

The spill, the worst ever in the United States, has shaved the stock market value of BP Plc (BP.L) by almost 40 percent since the April 20 blowout at its Deepwater Horizon rig. The accident killed 11 and left as much as 40,000 barrels a day of crude flowing into the Gulf.

A number of countries, including Canada and the United States, are reviewing regulations governing offshore exploration following the disaster. New rules haven't been set but it's likely companies will face increased scrutiny and greater delays in their offshore operations. No one yet knows what the impact of additional restrictions will be.

There are a whole lot of 'what-if' scenarios going around the street right now, said Chris Feltin, an analyst at Macquarie Securities Canada. Almost everybody has some exposure to the offshore and they are going to face increased scrutiny.

Five of Canada's eight largest oil and gas producers have significant offshore operations, though only one, Nexen Inc (NXY.TO), operates in the Gulf of Mexico. It's there that the greatest impact will likely be felt.

The Obama administration has imposed a six-month moratorium on new deepwater exploratory drilling in the Gulf and new rules for operating in the petroleum-rich region.

All the companies that are involved there will be anxious to see if (the moratorium) is extended or some other sort of moratorium will be enacted,' said John Kinsey, portfolio manager at Caldwell Securities.

The drilling ban has had an impact on companies that operate in the Gulf. On Thursday J.P Morgan Securities cut the price targets for many of the offshore drillers it covers. [ID:nSGE659OHL]

However the big Canadian oil companies that have offshore operations -- a list that includes Nexen, Husky Energy Inc (HSE.TO), Suncor Energy Inc (SU.TO), Talisman Energy Inc (TLM.TO) and Canadian Natural Resources Ltd (CNQ.TO) -- haven't seen their shares suffer as a result, though most of the stocks have weakened because of falling oil prices.

Canadian regulators have also been more accommodating than their U.S. counterparts on allowing deepwater exploration to continue. Last month the province of Newfoundland and Labrador, home to all of Canada's offshore oil projects, allowed Chevron Corp (CVX.N) to begin drilling an exploration well in waters nearly twice as deep as the BP well, though with toughened conditions and more frequent inspections.

As well, the offshore operations of most of Canada's petroleum companies make up a smaller part of their production portfolios than is the case with some foreign companies. Nexen produced 9,800 barrels of oil per day from the Gulf during the first quarter, less than 5 percent of its production of the fuel, though developing promising finds there now is likely to be delayed.

Suncor uses its offshore production from platforms off Newfoundland and the North Sea to fund its growing oil sands production. Those assets produced 160,700 bpd in the first quarter, 28 percent of its total production, but the company has few plans to engage in the risky deepwater exploration that backfired on BP.

While the Canadian operators haven't seen much impact on their shares from the spill, the BP experience is a cautionary tale for investors. The massive drop in BP's shares following the accident has easily topped the estimated costs of the clean-up and civil penalties. It serves notice that operating offshore can bring significant costs that are sure to grow in the coming years.

We really haven't had a pullback or weakness in step with what we've seen in the U.S., Feltin said. But we anticipate that offshore producers globally will see higher insurance premiums and delays in project timelines.